Runic Games released Torchlight for the Mac on May 2010 on Steam. It was built by Travis Baldree, Max Schaefer, and Erich Schaefer; Max and Erich were co-designers of both Diablo and Diablo II. Blizzard's own Diablo III was still two years off and people were chomping at the bit for some looting slashing gameplay. Torchlight delivered.
I loved its World Of Warcraft -esque cartoony style and starightforward mechanics. The story was pretty shallow, but it did the job, connecting deeper and deeper levels of randomly assembled dungeons. The only complaint I had with it was the lack of co-op/multiplayer. It was an entirely single-player affair.
Torchlight 2 arrives with that problem solved. Now I can crash through monsters and dangers with my friends, looting and slashing to the wee hours of the morning! It is only available on PC as of this writing, so those of us waiting to play it on our Macs will have to wait for a port... but there's always Bootcamp ;)