Steam Summer Sale 2013

So should I get both? Is there something I'd miss out on if I didn't play the first one?

They do have an overarching story, but you really won't miss much by just picking up the second game and not the first. Torchlight 2 is superior to the original in every way. The story isn't that complex either, you really could just read up about anything you don't understand if you truly care that much about the game's story.