Well, for the last week and a half I've been periodically playing Hellgate: London. As the first game from a bunch of people responsible for Diablo II who left Blizzard to start a new company, I've been waiting for it for quite a while. It's really been giving me mixed feelings, though.
I think that if you enjoyed Diablo II, you're going to like Hellgate: London. That's the bottom line. The basics are the same; you kill a ton of things, and then you loot bodies and then you kill more things. Actually, I think it's even a little faster-paced than Diablo, and I'm definitely preferring the first-person and close-third-person perspective to the isometric Diablo look.
But really, I don't think that the game is ready yet. Maybe wait another month or two. Get Gears of War and Unreal Tournament 3 and Crysis and any number of other cool-looking games coming out around now. Then, check out Hellgate later. It's beta-quality. It's not ready for release. It crashes, leaks memory, causes video driver failures, and has pretty terrible performance. The core gameplay is great, but the whole package isn't there yet. The story is pretty dumb and the characters are annoying and totally forgettable, but those things are pretty acceptable for an RPG/FPS hybrid. They have lots of plans for long-term subscription content, and I'm pretty confident that the game will be much more stable and enjoyable in a few months. World of Warcraft today is FAR, FAR better than it was when it launched, after all. I've already started Hellgate, and I don't really plan to stop right now, but I think after one play through I'll be taking a hiatus.
If you liked Diablo, you have to check out Hellgate. But I don't think you really need to now.