Demos in 5 Minutes - Overlord 2
OK, so a bit of an oldie this one, but hey it was late on a Saturday night, I'd just finished my second playthrough of New Vegas and I had a couple beers on the go :p
Overlord 2 came out last year (and apparently has some kind've expansion now I believe) and comes out of the CodeMasters bag of tricks. You can get the demo from BigDownload, FilePlanet, and Steam (and a few other places too), and I'm led to believe the demo is also on XBL (*shrug*). It's basically a hack & slash game with the addition of being able to control minions to do some/most/all of your fighting. There's some puzzles, some risible moments, some horrific Scottish accents, and just for good measure a giant yeti who reminds me of my ex ..