What I really liked about it is.....
....how the game was basically split up into three "sets" of room: one with GlaDoS, one in the 60's Aperture Graveyard, and one with Wheatley. They were different types of puzzles so it's not like you were playing 7 hours of the same basic type of puzzle. That helped a lot.
The one bad thing: you could remove Chapter 7 completely and it probably would have been a better game. It just took too damned long to get out of the 60's graveyard. The same way it took way too long to actually leave the facility at the end of the first game.
Was it worth $60? Hmm, maybe not. Is it worth $40 (what I paid)? Yeah, I'd say that's a good value, considering you get the 7 or so hour main game and the 4 or so hour co-op game. And it is a very good game on top of that and a great extension of what they started in the original. And I'm happy they didn't force multi into it, it would probably be borderline unplayable. But it certainly was missing the challenge rooms. That should be put back in with, say, weekly rooms added to bring you up to 50 or so with some leaderboards (Valve wants to give it to you for free, hopefully Sony and Microshaft would allow them to do that). That would not only add even more value as a full-priced game and extend the amount you play it.
And what the hell was it with them removing the ability to start part-way through the chapter or at a specific room? That was just weird