I'll tell you what I'm playing. Oblivion. I finally bought it yesterday for the PC and it is beyond my expectations. It's my first venture into the Elder Scrolls mythos, and so far it's been great. I've logged several hours in on it so far which, basically means I've yet to do much of anything. But I can sense greatness when I see it.
Want to know how great? Read this non-review, review at GamersWithJobs.com. It's actually worth reading even if you're not interested in the game because it's just a fine piece of writing and also will give you insight into how engrossing a single-player game can still be.