To me, a sequel has to be at least as good as, and with mechanics that are up to par with, the original. It's a really bad sign when the sequel takes significant steps backward. Case in point, the original's levels were sprawling and complex. The follow up's diminished level size (yes, I understand why this was done) can only be viewed as regression.
Yes... I KNOW. I am not saying it wasn't dissapointing and I know it should have been better than it was as a sequel to Deus Ex.
Still, none of that means it is not a worth playing and good game for other reasons. Same with Oblivion... crushing dissapointment following Morrowind, but still worth playing for me as an open world hack n slash.
I am not saying the game shouldn't have been better or different, it should have been, but that doesn't mean it is a total loss like you guys seem to say it is. It can still be a fun game despite not being the game it should have been.