It rivals A Song of Ice and Fire for the top spot (but actually has an end!), and I think it exceeds all the Sanderson, Rothfuss, & Jemison I've read (my other 5-star picks). Tolkien can't be compared, that's a separate category altogether.
George Martin once said "There are two types of authors: Gardeners and architects". The First law trilogy has the best of both: Epic, realistic, character-motivated plot (à la George Martin), but yet somehow also crisp and satisfying(sort of) plot lines, where everything seems to tie together at the end (despite the length).
It's Grim and Cynical. Subtly subversive to genre tropes. Ruthless and Realistic. It might be the most violent book I've read. I had no idea it was even possible to write fight-scenes in such a gritty and visceral way. But they don't feel extravagant or unnecessary.
I'm so pumped for Abercrombie's later books. I hear they are as good or better.