GameMethod decided to preview Hellgate: London. Here's some of what they thought:
In the game you’ll meet up with other humans in the tunnels, equip your
character with weapons and armor, then form a party and head out into
the demon-infested wastelands above. Through the game’s missions,
you’ll work to do your part to push back the demons and save the human
race. During the game’s single player campaign, you’ll meet up with
fellow survivors underground to gather intelligence and rest; whereas
playing online, you’ll team up with other players to wreak havoc upon
the demons residing above. As in other massively multiplayer games like
Guild Wars and Phantasy Star Online, the central
“town” areas (tunnels in this case) will be the only places where
you’ll see a large number of characters; once you leave town, you’ll
rarely encounter anything other than demons.
The multiplayer sounds kind of like Diablo's online part, which isn't surprising considering it's the same people making this game.