I remember playing the original TimeShift demo one or two years ago. It was a pretty boring, generic first-person shooter, even with the time effects. I thought it would be released and quickly forgotten.
About two weeks before the game was to ship the project leader decided that the game sucked and he wanted to try again. The team that did Resident Evil 4 did this as well, and RE4 became a way better game because of it, so I thought this was a good decision.
Well, it definitely was a good decision, because I haven't played an FPS I've enjoyed this much in a while. They redid the game with darker, grittier graphics, for one thing. Normally this wouldn't be a good thing, but the pseudo-cartoony graphics of the original demo quite frankly sucked, and the new style suits the mood much better. The whole atmosphere of the game reminds me of a grainier Half-Life 2, and anything that reminds me of Half-Life 2 is pretty sweet. Weapon design is fantastic. The environments are destructible, which is awesome. Bodies are gibbable, which is also awesome. And the Time Reverse function makes my head hurt it's so cool. There are a number of other small touches that make this one great.
Lesson learned: if your game needs a year or two for an overhaul, do it.
(Go download the demo now.)