Most likely Red Alert 2, I prefer larger scale RTS games like the Total War Games or Supreme Commander, but Red Alert 2 provides some simple fun and wacky units to play with.

With all the games I bought recently the only ones old enough are Desu Xe WI which I played within the last month
If I treat Invisible War as its own game, rather than a Deus Ex game, is it decent?
I remember Spartan, it was a ton of fun, I never managed to finish it though, I got stuck on the level with Achilles' Spear in it, the tomb one.