I played C&C Generals for some time, but IMO it's no match for WC3. I got bored of Generals after a couple of weeks...
As for Tiberian Sun and Red Alert, I never really played them.
Anyway, if you are obsessed by guns and tanks, you'll be happier with generals...
At least the sides are diffrent in C&C. I tried to play Rise of Nations, but I find the civilizations not really different from each others.
~Dark Cupcake of the Sith