I personally find cover flow on the classic (I have one) to be pretty useless. Fun to play around for a few minutes, but not very practical when you have a lot of music. It probably works better with a touchscreen interface like the iPod Touch or iPhone.

The newer games on the iTunes store (like Peggle) will only on the classic and the video rentals as well.

The only way you can find a 5.5g iPod is if it's older stock or second-hand, so keep that in mind.