The only time my cold sorceress was in danger early on was against that Amazon chick (Blood Raven?), since she moved really fast relative to my shot speed. Aside from that it's just a matter of not getting surrounded, so I much prefer cold to fire or lightning for the freezing effects.
Oh, and Duriel kicked my ass, but that's mainly because it's the one spot where my computer slowed to a crawl.
In Hiatus:
Gemstone IV
None of these require anything really over the top, hardware-wise, or time commitment-wise. Jump in and play, and quit when you want. I'm all about nuturing my short attention span.
Lag is a problem on older machines. The trick to killing Duriel with a cold sorceress (or a fire druid) is to get boots that give you a faster run/walk (Treads of Cthon are good) and then run circles around him while casting Blizzard (or Fissure, for the druid). He can't quite ever catch up with you and he just spins around taking damage until he dies.