I can't say torchlight is better than Diablo. It's different, but that doesn't mean it's worse either.
While Diablo (especially the first one) felt more rogue-ish, mostly being that you usually went alone, had limited resources, and you were careful most of the time except when you were leveled up enough and had good enough equipment to get you by.
Torchlight 1 is a little more lighthearted, although some mods can make it outright evil to play. Torchlight 2 feels more like a singleplayer MMO, which isn't bad, but you aren't nearly as careful. I remember playing Torchlight and enjoying it, sending my pet more often back to sell crap, and then i got turrets and just started throwing turrets everywhere and doing just fine... The largest annoyance of Torchlight 1 is that if you go to the extra area (infinite dungeon) and you die, going back down 20 levels is just a pain, while adding a jump point every 5 levels like the main game would have been nice.