I couldn't wait for reviews or impressions, so i went ahead and bought it yesterday.
Thought i write down my own impressions to help out people that are still on the fence.
Been playing it a couple of hours and reached Level 6.
Graphics:
The pixel-art is just beautiful. Characters in cutscenes are drawn very pretty and detailed.
Environments are also very detailed and atmospheric. Though the six levels i played so far didnt have much variety, they have all been forest/ruin maps until now. The game runs fluid at 60fps and looks great in handheld mode.
Have been playing it exclusively in handheld mode.
Music / Sound:
Ambient music during the Levels, nothing to special (yet). The camp has a nice melody that stood out for me, but that is it.
There are no voice-overs in cutscenes, only some short samples like "hahaha", "alright" or other noises.
Opening sequence is also text only.
Gameplay:
Game can be divided into 3 phases:
Camp
Before choosing a level you can upgrade your towers/traps or buy new gear for your heroes.
After a few missions you can also buy upgrades like more health or inventory space.
Tower upgrades need RP and characters need currency.
Rp is rewarded after missions and in dialogues.
Currency drops as enemy loot and also rewarded after missions.
Exploring
You kill enemies, solve small puzzles and collect 4 collectibles before reaching the tower defense part.
Sadly the only thing you find are collectibles and currency. No upgrades, tools or weapons.
Which is a let down for me personally.
Tower Defense
At the end of the level you have to defend some kind of macguffin. You use your towers, traps and heroes.
Each hero has a specific resource to build stuff and you find more resources from spots that re-spawn in-between phases.
For example:
Clu uses flowers for bombs and spikes, while Bart has stones for building walls and turrets.
After a few levels you get the ability to mix both.
For example:
Bart builds a wall, now Clu can build a bomb and combine it with the wall, which results in a spread turret.
Heroes also have different abilites and weapons.
Clu uses ranged weapons and has a dodge, while Bart uses close ranged weapons, can block and can use his hammer to build faster or repair stuff.
After 5 phases you beat the level. Perhaps later levels will have more phases, i dont know yet.
Plus each level so far had some kind of environmental twist you can use to defeat enemies, which adds a nice variety to defending.
Singleplayer / A.I.
I have been playing this game completley alone and after beating the 6th level i will stop doing so.
Dont get me wrong, its not like its super hard alone, but its kinda stressfull.
I really think singleplayer was an afterthought and could use some balancing, like more time in-between phases.
It may sound harsh, but i think the A.I. is completely useless.
The A.I. will shoot stuff and repair your buildings, but at a very slooooow rate, you are better off just switching heroes and doing it yourself. There a mountable turrets later on you can aim and shoot foes with. Yes, the A.I. will mount and shoot, but will only auto fire in a straight line without aiming. Even if there are no enemies in front of them.
That point was very frustrating for me.
Replayability / Longevity
You can replay levels as often as you want to collect missing collectibles, fullfill objectives or just to farm.
Each level has 4 collectibles.
There are 64 collectibles in total, therefore there should be around 16 Levels.
But i am just speculating.
TL;DR:
(+) Beautiful artstyle, detailed characters and environments
(+) Fun gameplay mix of platforming and defending
(+) Runs fluid in 60 FPS
(+) Looks and plays great in handheld mode
(+) Fun coop
(-) Exploring is linear and not very rewarding
(-) A.I. is useless (imo)
(-) Balancing issues in singleplayer
Edit: TL;DR, formatting and spelling.