I won't join the chorus of pundits who've declared PC gaming "dead," but I will say it's pretty bereft of high-profile titles these days.
On the other hand, if you're into real-time strategy (RTS), there's absolutely no better platform than the PC. And many would argue that there's no better RTS experience than the Command & Conquer series.
Normally $29.95, Command & Conquer 4: Tiberian Twilight is now just $17.97 when you download it from the EA Store.
Is C&C 4 the best game in the series? In my book, no--that honor goes to C&C Generals. But for 18 bucks, you'll enjoy some gorgeous visuals and spectacular online action. Well worth the money, IMHO.
If you're more into first-person shooters, you'd be crazy to pass up Battlefield: Bad Company 2, also on sale for $17.97. Gamespot awarded this somewhat-overlooked sequel a 9.0 rating and an Editors' Choice. Their take: "Battlefield: Bad Company 2 boasts a fast-paced and thrilling campaign, as well as some of the most immersive and exciting multiplayer action around."
And there's another point in favor of PC gaming over consoles: it tends to be way cheaper, especially if you wait a few months for sales and price drops. (Best price on the Xbox 360 version of Bad Company 2: $39.75.)
Personally, I just need to find the time to play the games I already have. Anyone know where I can pick up a 29-hour day?