Bioshock was too long, or rather: the content after the Ryan reveal wasn't as interesting as what preceded it. I'm not saying the game should have ended at that moment, but it was an important plot point and you kind of expect the game to go from there, but it didn't. The areas post-Ryan looked like they could've come from a dozen other games (gritty urban environment, hospital), in contrast to pretty fucked up areas like the Medical Pavillion, the gardens (forgot the name) en Fort Frolic.
After that came a fucking boss battle of all things, and a poor one at that, so I feel the game didn't end on a particularly good note.
I may come off as negative here, so let it be known that I thoroughly enjoyed BioShock up until that point and I was ready to sing its praises with little ifs and buts, but then the game overstayed its welcome.
That is why I welcome experiences like Portal, Gears of War and other shorter campaigns. Don't pad your game with content because you have to cater to the 'it's $€60 so I better get my money's worth' crowd.