Nothing's exactly like Arcanum, of course, but I have some ideas. It sounds like you want to stay in an unusual fantasy or semi-fantasy setting.

If you haven't played Planscape: Torment yet, that might be a good choice. There's an enhanced edition in the works, but I'd probably grab it before that comes out so you don't have to get it in a bundle with the new one. There's really nothing that needs to be enhanced, you see.

You could try Temple of Elemental Evil. You've played Arcanum and Bloodlines. ToEE is Troika's only other game. It's flawed in a lot of ways because it's based pretty strictly on a classic PnP Dungeons & Dragons module, but it's got great combat. It's sort of the opposite of Planscape Torment which has a great story (arguably the best story ever in a cRPG) and not-so-great combat.

If you don't mind the simple graphics, you could check out the Geneforge series from Spiderweb. They look kind of cheap at first glance, but they're actually really good.

Someone in the other thread mentioned Arx Fatalis. I just played that recently and I really enjoyed it. It's first-person so it's a little different, but it's got a very interesting setting and magic system.

That should get you started, I guess. I feel like I'm forgetting something, but if I think of it I'll let you know.

EDIT: Oh yeah, I remember now (30 seconds later). You might take a look at the new Shadowrun games from Harebrained Schemes. I didn't like them quite as much the others I've mentioned, but a lot of people do. Dragonfall is probably the best one.