Steam already has the demo atm and the torchlight website will have it soon.
Mac version is being worked on.
The game's art direction, while not all gritty gothic and serious, is still fabulous. The music is done by one of the guys who did music for diablo (Tristam anyone?), the creatures/characters stand out against the backgrounds, and it all seems to fit perfectly together.
While it may seem a bit cartoony, it's better that than trying to fake realism with low poly models. WoW can be pretty entertaining -depending on who you are- even though it's 'cartoony'. (A friend of mine describe it as "Diablo and WoW had a baby)
While the game probably won't ever surpass Diablo 3, it was never meant to. They don't even want to try, and one of the points everyone says is that it's a cheap, fun, and fulfilling game for $20 that you can play until Diablo 3 comes out.
The extensive modding capabilities may not mean much to you if you don't mod, but even so, other people mod and eventually someone will create pure gold. It could be a new class, or even a new campaign, or even basically a brand new game.
So if you have $20 now, or the next couple months *Holidays, people*, it's well worth a look into.
People do still play CS1.6 you know
*Yes I know I'm totally shilling the game, but hey, I haven't found a game I like for sheer potential alone this much since I saw dwarf fortress.