I picked up Torchlight II (Better than Diablo III IMHO)
I got Diablo III for free because I signed up for the World of Warcraft annual pass last year. I was not impressed with it. Basically it was nothing more than running around and spam clicking on crap until it died, then picking up piles of gold and crappy loot. I ran through it once, but haven't touched it in months. I never played the first two, so I don't know if they were any better.
Also, you might want to check other game download sites as well. This site here offers a good list of what is on sale at steam and a few others:http://www.steamgamesales.com/
Also, Amazon is running some really good deals right now. I just picked up Bioshock I and II for $5 total.