Trine was a fun little fantasy arcade scroller. Side to side action. A platformer.
Torchlight is a dungeon crawler in the vein of diablo. Lots of equipment dropping, items to get, etc, as opposed to the more platformer-style of Trine.
Very, very different games that happen to be set in the same fantasy genre.
Torchlight is a highly overrated Diablo 1 clone. The game has barely any story. The side quest system literally repeats "Kill the monster on level 5" "Kill the monster on level 10" "Kill the monster on level 15" etc.
The game has some okay graphics and the loot system is decent. If you enjoy looting corpses for a slightly upgraded item over and over in a noxiously repetitive manner then I say go for it.
Five people in my office bough the game. I played it on very hard and beat it. I was the only person to reach the end despite everyone else playing on normal difficulty.
I beat the game out of spite. I never felt so angry at a game before but my sheer hatred of it drove me to finish.
I guarantee most positive reviews come from people who did not finish the game. It's just not fun after the first 10, 20, 30, 40, infinite floors in the same dungeon.
I enjoyed it a lot. Sure it's not a AAA title - but it's good, mindless fun. Especially given its extremely appealing price point. (And, yes, I haven't finished it.)