As a huge fan of Diablo I also have a lot of respect for the Torchlight series which offers very similar experiences to that of Diablo.
Writing off this game as a simple Diablo clone wouldn't be doing this game franchise justice as it takes everything about the action role playing genre and adds it's own spin on it. It's a franchise of spent hundreds of hours in and I know I'm not alone with plenty of people on Xfire and Steam racking up similar large scale numbers.
I love the casual sort of gameplay that Torchlight popularised as it doesn't require as much time as the more hardcore Diablo series to make progress. It's the kind of game I feel comfortable jumping in for 30 minutes at a time while longer sessions are best reserved for other games.
On this page I'll be providing a brief overview and comparison of the two games that should serve as a helpful reference for Torchlight and non-Torchlight players alike.