Everything from Dark Side to The Wall is classic Floyd. The reason why people don't like The Wall over Dark Side is because it's a much colder album. There's the clear absence of the funky guitar riffs that were present in the previous three albums. My only gripe with Dark Side and The Wall is that Waters and Co. put too much effort into writing the lyrics. I think the music could have been expanded to touch on deeper concepts. Wish You Were Here is the perfect balance between music and writing, as is shown in Shine On You Crazy Diamond Parts 1-9.

The Wall is conceptually brilliant, though. It's The Concept Album of all times. Pink Floyd was an awesome band right up until the end of The Wall tour.

p.s. Listen to Echoes on the Meddle album. It's just as good, if not better than anything they did after.

EDIT: Oh, and Another Brick in the Wall Pt.2 is highly overrated. All it is is an exacty copy of a Disco beat.