Dungeon Runners is a free* Diablo clone by NCSoft (makers of Guild Wars). I've had it downloaded for quite a few months but for some reason never played it. Just a couple of days ago I was reading the FAQs and forums about it and it seems exactly like Diablo (which I really liked). So I got excited and wondered WTH I hadn't played it... I mean a free Diablo clone (I sold D2 + LOD long ago)... hell yeah! Still have yet to play it, but I will today.
* By free, I mean yet it is free to download and play, but there are a number of premium features that require a $5/mo subscription. I'd think if its a game you intend to play lots of, the free version might be too limited. The recent patch added dungeons/areas for only premium members. I forget the other restrictions but one is the quality of items you can pick up. I suspect the later dungeons might get more difficult with the limited/free items.
For more in-depth play, you could go with Guild Wars. It requires no monthly fee but is similar to Diablo in that you only really play/party with a small number of players, so it's not a MMORPG. GW is not the same as Diablo/DR really, in that it is not a click fest. It is more slower paced and less focused on getting loot drops.
Another option is Titan Quest. I'm not sure how the online play is but the SP demo I played was great. You could probably find the original TQ for fairly cheap now.
At the least, you can try out the free Dungeon Runners, also Mythos beta if it is open. If you find yourself wanting more of a slower RPG gameplay, maybe you can find a guest pass for Guild Wars. My roommate just bought a couple of $1.99 trial discs for GW (all three), WoW, and FF. They might only have 10-20 hours of gameplay/10-14 days, but it is almost nothing to buy and you can see if GW is something you'd want to buy.
