It seems that the Torchlight MMO is on hold for now, because instead we're getting Torchlight 2!
From runic games site is a list of key features:
The video looks pretty nice in my opinion. There are a lot of new monsters/areas it seems and I really like the look of the outdoor overworld. Also I dont think any information about the 4th class is out yet (or if all 3 original classes are going to stay).
EDIT: I managed to find an interview that gives out a bit of info on the game. Here's a link to the interview:
If you're not interested in reading the whole thing here are some important highlights: