Supreme Commander is worth a shot, if only to marvel at the game's ability to truly escalate in size and scope as the game progresses. It's damn fun entertainment and I loved the (over 100) online games I played between it and Forged Alliance. Campaign is middling, skirmish is pretty entertaining, online play is very good with a mostly non-asshat (but expert grade) community.
Hearts of Iron 2 is the WW2 game that people who find Civilization IV inadequate except for "casual gaming". It's very playable and understandable if you put some real time (not talking a few hours, I'm talking fighting game style tens of hours of reading and a lot of experimenting/playing to really understand) learning it. You're rewarded with the finest strategic level game of modern warfare available on the PC that can be played for literally hundreds of hours. As a bonus, you'll along the way learned one Paradox game, which makes learning equally stuff like EU3, Victoria, and Crusader Kings.
Shame that Road to Hill 30 doesn't work in Vista. That's a fun game, even if squad combat in Normandy is more than a bit cliche (unless it involved the Commonwealth) at this point.
