There's been some great Flash games that take a 3D concept and turn it into a fun and addicting 2D experience.
Portal comes to mind as one but we have another one here. Head on over to
Bourne Games and play a 2D side scrolling version of
Mirror's Edge. It's very nice looking and has some awesome animation. Right now it's a beta so expect a few quirks here and there but so far I've had a blast playing it and I can't wait for the final version to be out.