Titan Quest tops my list too, if you don't have massive stability issues (rubber banding) in Immortal Throne expac, it corrects the few complaints fans had about the original and adds several new areas that are fun as hell.

Given that you have what, 8 character classes and you can dual class, that's a lot of potential flexibility.

If you're a hoarder, there's a mod that allows you to have unlimited storage (it's actually a trainer, that just keeps the ids of the items you put in it and count for you, but will only generate items you've stored in it - there are other mods to give yourself whatever you want in the game, but that's no fun).

Now, the real fun is getting your ass handed to you because that Minotaur just spawned with a very powerful magic axe, and he's using it on you!