Generals Zero Hour was a little okay, but it's more fun with the All Stars mod.
Renegade is fun too if you find a decent server.
Red Alert 2 is okay, but YR is a letdown.
Tiberian Dawn, Tiberian Sun, and Red Alert 1 I haven't played.
If you have played the other games already you probably won't like red alert 1, I played it when it first came out and is was awesome sauce. Then not too long ago I reinstalled it and hated it, just too hard to like after playing all the newer games.
This is even more true of Tiberian dawn.
If you liked RA2 you may like Tiberian sun but don't get your hopes up, it's not nearly as good.
Had you played the series chronologically you would see the progression of technology and game play over a number of years and may have really enjoyed it. I played them as they came out so I did get the see the whole wow factor as each new game blew away the last.
