So, tl;dr first. It's a solid B-tier FPS (I would rate it at B-) that's part 90s old school shooters-like and part Painkiller or Serious Sam-like. The overall experience is rather uneven and lacks polish. Its occasional highs are good, its less occasional lows are annoying and frustrating. Most of the time it's okay. Worth a try for old school FPS lovers, certainly.
If you liked the first episode and feel like the next episode is a letdown, and the next one is also iffy, I would recommend powering through. The game does have good bits. But if you want solid, consistent experience that's at least on the level of the first episode, and ideally more - it's probably not a good fit for you.
Level design and quality are highly variable. Episode 1 is probably the most solid one and it's the one with the most 90s-like design. Episode 2 and 3 feel like and earlier work, and Episode 4 feels similar in that regard. All three share a higher than usual (for this game) affinity for boring rooms, long hallways, more linear style design and boring level geometry. Episodes 5 and 6 are more solidly made, but still share some of the same flaws of other episodes. These two have a verticality gimmick. Episode 7 is the standout visually, but unfortunately it runs out of steam somewhat quickly and gameplay wise it offers nothing new. Still, the visuals are stellar.
I love 90s style style design and I'm really not a fan of Serious Sam or Painkiller style design. My general feelings for Amid Evil's levels is that they have about 70% of Painkiller's DNA and the rest is old school 90s DNA. So not fully arena style, but leaning towards.
The levels with a verticality or platforming gimmick share a common problem - the air control sucks. The jump height is too low and the player bleeds off momentum too slowly when movement keys are engaged. To clarify - if jump forward when running and press S (the key for backwards motion), the player's velocity would drop off relatively slow. Try it in Quake - it's near instant, and Quake's jump height is higher. What this means in practice is that it's too easy to overshoot and pin-point landing precision while in the air is impossible at certain distances. The game needs to up its jump height, significantly up the rate of velocity reduction on player's movement commands, and maybe turn the gravity a tad lower.
Another major problem with verticality (Episode 5 is the biggest offender) is that the level designers love narrow ledges. It's pretty easy to fall down and lose a ton of progress. So unless you fancy spending a minute or two getting back up, you'll be constantly quicksaving just to be sure that you don't have to waste time if you fell down. Adding a double jump to the above suggested improvements would've alleviated this issue greatly because you'd be able to jump back up (provided you do it quickly, of course). It's not something that can be easily added because naturally, it will break some of the level design.
In general, a lot of the levels feel needlessly large and the scale feels off. By scale I mean Alice in Wonderland sort of scale - you feel like a tiny dude in an environment build for much bigger dudes. Except that the enemy models often feel to small as well. Anyway, this "giganticism" gimmick, let's call it that, can be extremely obnoxious at times because if you need to backtrack, depending on the level you might find yourself running through huge boring hallways and massive rooms that don't really have much in them.
Speaking of, the hallways and rooms don't have much in them. The game's interactivity mostly boils down to running around, platforming and killing bad dudes. Levels can be visually exciting, but there's often not much creativity with regards to gameplay or geometry. Sure, the last episode of the base game is cool. The two verticality - centered episodes are also cool and have some interesting geometry and visual design. But it's just not enough. It's too basic, and there are too many other maps with far blander design. If every episode had the creativity of the base game's last episode - now we're talking.
And as for the newly released Black Labyrinth - the first Episode is kind of okay, would've fit in the base game fine I think, not as good as its better episodes though. The second episode was my least favorite out of them all by far. Very linear, very Painkiller-like vibe, lots of gimmicky platforming. I didn't like the enemy design at all. The dudes spewing air vortices are visually annoying, the jumping dudes are flat out obnoxious. The ghost face flying enemy felt poorly balanced - too mobile, deals too high damage, its projectiles are too fast, and too much HP. Arrow dudes were annoying, but sniping arrow dudes are just poor design. Too many of those. The dudes with the giant shield though... oh boy...
Gunplay is of the "not great, not terrible" variety. Serviceable, but nothing beyond that. Most of the weapons have a noticeable and extremely annoying delay. Now, normally, upon pressing your firing button, you expect the weapon to fire. Maybe there's a windup for balance reasons or as a gimmick. But generally, you expect it to go off. Not in Amid Evil. In Amid Evil, the weapon does a bit of an animation, and only then the projectile goes off. What this means in practice is that pressing and holding the weapons fire button is often the optimal strategy. That's because it allows you to get accustomed to the timing between shots and aim at the precise moment.
The balance of the weapons is really odd. Your "pistol" weapon, the wand, is not only perfectly viable at any stage, it's often one of the strongest weapons due to its rate of fire and homing projectiles. The "rocket launcher", while cool on paper (I mean come on, shooting tiny planets is really cool), is probably the weakest weapon of them all. The problem with it is that the AOE of the explosion is pitiful, the direct damage feels too low, and the projectile itself feels too small, you have to be extremely precise in your aim (remember the animation delay the weapons have?). The "chaingun" is mostly crap, but it can be occasionally useful if you circle strafe and track a high HP enemy, or for its AOE attack (the problem here is that it's hard to reliably pull off). The sword is okay, probably the best balanced weapon. The Star of Torment is the "we have Flak Cannon at home". Well, it's not bad, it does have an unusually high damage, but the animation delay and the narrow cone of fire is what makes it a bit iffy. It's a very viable weapon in the game, but I just can't help comparing it to the Flak Cannon, it's so much less satisfying to use. The BFG is kinda cool, but I rarely used it. The Scythe is very cool visually, but in terms of gameplay it's just stupid, it's too primitive of a weapon with far too much damage. Axe I never used. The gauntlets suck. Sure, they're powerful, but you'll inevitably get chip damage, and chip damage can and will eat away at your HP quite fast at times.
Enemy roster is not great either. The gimmick of the game is that it has different enemies for each episode, but in practice it has the same basic enemy types with only minor variations. Some a bit more varied then others, but it all follows the same basic logic. There's the cannon fodder enemy - they run up to you Serious Sam style, they have low HP, and they're highly mobile. There's a ranged enemy or two. A mandatory flying enemy with high mobility. Then a more tanky enemy or two, and a super tanky one you'll occasionally see. There's no interesting interplay between enemies like in Doom 2, the AI is pretty braindead and they're all simply trying to kill you with no real synergy.
A special mention goes to the shielded dudes in the Black Labyrinth DLC. Did you think Hexen's Slaughtaurs are peak enemy design? Did you love the idea of Marauder's shield in Doom Eternal? You'll love shielded dudes. Okay, okay, they're not really that bad, you can get them with the rocket launcher, but the timing window is too short and they're still annoying to deal with. You can circle strafe them like an asshole and gauntlet them too, but it's also hella annoying and will deal some chip damage to you. Worst enemy in the whole game by a huge margin. Thankfully, it only appears briefly.
Due to the unusually large scale of the levels, most of the combat is long to medium ranged. Sadly, about 90% of the time the more challenging encounters are all about either circle strafing and firing pretty much any available weapon at the enemies or running backwards (thus kiting them) and also simply firing something in their general direction. There's no real strategy behind it and the tactics are of the primitive Serious Sam and Painkiller variety. The other type of encounter are the throwaway enemies that present zero challenge - two or three medium HP guys teleport in (or run from the now opened door) and you dispatch them with absolutely no risk of any kind.
Only very occasionally does the game put you in slightly sticky situations, but the problem is, ammo is usually fairly plentiful, and so are the souls. You'll either use the power up or the 7th weapon (maybe both). I've finished the base game and the DLC on Hard and very rarely did I feel the need to use the soul power up or the 7th weapon, and even then, it's more to speed things up.
The only time the game gave me anything resembling real trouble was in one of the later Black Labyrinth DLC levels where I was very low on ammo and health and the game spawned a bunch of flying enemies underwater. For some ungodly reason, they were just as mobile underwater as in the air, while the player character was not, of course. Coupled with the low HP and ammo, it took a while to get out of there. But that's an edge case really.
I played through the base game with carry-over weapons and Black Labyrinth with pistol start. My recommendation, hands down, is to play with pistol start. Though even then, the game almost always give you plenty of items so that you'd be hoarding ammo and souls.
Speaking of difficulty, Amid Evil's difficulty settings affect several things including the number of enemies. Unfortunately, difficulty also scales the enemy HP. On Hard, aside from cannon fodder, enemies often feel needlessly tanky. Coupled with the game's fairly low difficulty and Painkiller-like combat, it made a lot of the encounters feel tedious. Higher HP enemies always took a shot or two more than they should have really.
