In my opinion, Diablo 2 is the perfect game of the genre because of three "speeds" - movement, leveling, and loot. I've played many of the other games in the genre (Torchlight 1/2, Titan Quest, Path of Exile, Sacred), and I feel Torchlight comes the closest. Titan Quest and Path of Exile are both noticeably slower in those three categories, which in my opinion makes them more difficult to get into (let me be clear, I'm a big fan of the genre and loved all of them on their own merits).
So in my opinion, it is worth it (I believe I payed 5 for TL and 10 for TL2). If you are a fan of the genre, I'd say its a title you can't pass up, and for that price it is a no brainer.
The right man in the wrong place can make all the difference in the world.
If you enjoy Action RPGs you will love Torchlight 2 - the skill trees for the various classes are diverse enough for you to make some interesting builds, and the monsters and environments are varied enough (both in appearance and abilities in the case of the monsters) to keep things interesting. Add in the "Synergies" mod, and you have a great ARPG experience.