Ha! I haven't done the Diablo series because I don't want pentagrams on my pc, but agree D3 will be big.
Did Everquest for a year because a client got me into it; it was cool to hook up with her and know what she looked like and was in Kansas while I was in Dallas. I was in the tunnel between Rivervale and Misty Thicket at 4:30AM on a Monday I was supposed to work with her that day and turned around and she was standing right behind me, not saying a word. Oops. It was pretty funny. Clerics rule, btw and I miss them being absorbed into the mage category - little McDibble was a BASHING cleric! Too social for me though.
If you want an excellent online game that's less well known, maybe try Aces High. It's a WWII flight sim, but you can drive a bunch of vehicles and even a PT boat. Was mainly a B24J bomber guy, but if I did fighters would drive a Russian Yak-9U. I had aspirations of ranking in the top 1,000 someday, but looked at the hours flown by the guy that came in first for the month. It averaged out to five and a half hours a day, every day for the entire month. That's when you give up trying to be number one. You'll need a headset, and some of the piloty lingo can be really fun.
For now, approaching the end of playing time with Skyrim, all main and faction quests achieved, and will need to move over to Mass Effect 3 (brutes SUCK!), Assassins Creed Brotherhood or maybe finish Crysis 2. I also spent a lot of time with Fallout 2, but never warmed to Fallout 3; the developers of Skyrim even said it was nice to finish Fallout 3 and start Skyrim so they could have grass! Will also keep doing Silent Hunter 3 (the best one), DiRT 3 and GT Legends. Someone needs to make a good old west shooter for the PC; Red Dead Redemption was console only.