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.
I don't know about version directly form Relic but Steam version can be run without internet connection and doesn't appear to have limited activations. ANd it certainly isn't patched too often to be afraid you'll miss something. I am not sure it had any in last year.
I would probably rate it as my no. 1 in hack'n'slash games. Path of Exile is better game and have incredibly extensive skill tree and fun season events but it needs interent connection to run and tends to lag because of it sometimes. Usualy nothing too extensive but it has its bad moments. If it had offline mode, it would be very likely the number one. I like bot T2 and PoE more than Diablo 2
Exile is free to play with microtransactions but most of it are cosmetic effects for weapons, armors, spells, etc. They also sell more stash slots but you get 5 I think for free and they are quite spacey.
@OP, no Torchlight 2 was never here. People were asking for it around release, hoping it could appear but it never did.