tinyE: When I bought it, a year or so ago, I was told there were limited installs. Now that came with the assurance that I could write Relic with my account info and they would give me more installs as I needed them. AND as near as I can tell you need to be online to play it. You might be able to get away with SP by unplugging your connection but you won't get any updates or patches or mods which are automated.
Elmofongo: In the end is it any better than Torchlight 1 or all 3 Diablos?
NOTHING is better than Diablo 2....NOTHING!!!!!!!!
That being said it's way better than Torchlight 1, and I love Torchlight 1. T2 is obviously bigger, better weapons, characters (Berzeker: think Wolverine on speed), and more than that it is loaded with gags and Easter eggs. Just for starters you can chose the head-crab from Half Life for your pet. Also early on you will come across 'One-Eyed Willie' from The Goonies. Nice little touches keep it fun.