Should I finish Torchlight before playing Torchlight II?

Having played Torchlight 1 and now some of 2, I'd say there's little benefit to having finished T1 for T2. The stories are only vaguely connected at the very beginning and there's no T1 spoilers in T2 so far. The T1 story was very small and narrow, T2 has a relatively broader scope, but it's still not very story driven.

Neither will finishing T1 help you play T2. While the controls are the same, T2 has a reworked class and skill system. The builds and techniques are different.

While T2 is definitely a direct sequel of T1, you have to realize, these are both games that focus on "kill everything that moves" and "loot everything you see". The storyline is only there to help players become familiar with areas and the enemies that arise from them, but isn't necessary play T1 over T2.

Honestly though, T2 is a completely reworked version of T1 that features a whole slew of new improvements, as well as dedicated modding support, etc.

Consider this, it's very much like the L4D series. While L4D had a storyline, and so did L4D2, the story lines were only vaguely connected, but the game was more about a zombie co-op game. This isn't to say the storyline was non-existent, but it's there to guide players to understand what's happening around them. Gameplay-wise, much like TL2, L4D2 is a very very nice upgrade to L4D, in that there are more weapons, more game modes, more special infected, and other nice sweets.

Basically, consider T2 over T1 as a nice upgrade, with more features than its predecessor. If you really really care about storyline, by all means, it doesn't hurt to play T1. If you really like gameplay, then I'd say it really doesn't matter.

Judging from the Torchlight II FAQ, it would probably be worth getting past the main story (Defeating Ordrak) before playing this game.

Years ago, the Heroes of Torchlight saved the world from the ancient evil, Ordrak. Now someone has stolen the essence of his power...

It looks like there is a tie between the storylines of these two games and that yes, I should complete Torchlight I first before starting the next game.

I'm not entirely sure how loose this tie is as the second game hasn't been release yet, however I'm just going to play it safe and complete the first game first (The way I assume the series is meant to be played).