Torchlight is an action-RPG, much like the classic genre defining game Diablo.
Unlike that grim, dark game, Torchlight has a comic-like style and while the gameplay itself is very similar, the feel is much lighter. It's not gory at all, making it much more suitable for younger players.
You begin by choosing one of three types of character - hunter, warrior or alchemist - and then set off on your journey. The formula is nothing new - talk to people, get quests, head into dungeons to complete them, while battling off various beasts along the way. If you don't enjoy RPGs, you won't like Torchlight either, but it's very well done. One innovation is your pet - you can choose a pet to take with you on your journey, which follows you around, and helps out in battle.
Controls are really simple, just point and click for movement, and left click to use weapons, right to use magic attacks. It's really easy to pick up. This means your time in Torchlight is going to involve a lot of click, click, clicking. Despite these very simple mechanics, it's really easy to get drawn into the exploration, fighting and questing.
Torchlight is a very cliched action RPG, but what it does it does very well, and is very accessible for newcomers to the genre.