As I've stated before, I'm in the beta myself and loving it, so I'll try to clear up any muddled thoughts on what the game is without breaking the NDA. You won't learn anything here you can't read on the official website or in previews across the web, but if you're here and you're wondering, I'll try to put as simply as possible.
So then, what kind of game is Hellgate: London?
Think of Flagship Studios' premier game as the bastard stepchild of Quake and Diablo. Only where most bastard step-children are disliked by their family for being so "different", HG:L shines because of its fresh take on a genre that hasn't advanced much in the past 10 years. It's part hack and slash, part shooter. Part balls-out action and part strategy rpg.
For those worried that an action RPG blended with a shooter will be too twitch for them, Bill Roper said it best in a recent interview with N'Gai Croal,
"If you're playing one of the hunter classes, especially the marksman, you're still going to be playing an action-RPG and still have all those role-playing things like leveling up and items, and skills, and you care about your character level versus monster level and all those things; but it has much more of an FPS feel to it.
Like the mechanics flow more that way because the higher the level you get, depending on what skills you take, there's a lot more concern as to player skill whereas the Templar classes and the Cabalist classes don't really rely on player's skill; your twitch skill specifically. The marksman class very specifically, the higher level you get is more built to have more interest for FPS players because, depending again on the skills that you take, it becomes very dependent on player accuracy; and you get benefits for that."
So worry not, fellow shooter-inept gamers. There are 6 different classes, two of which are hunters, and those are the "FPS Classes". The others rely considerably less on your aiming. This one won't force you to suddenly become a masterful mouse tactician. Hellgate: London, above all else, is an Action-RPG with hefty online support (guilds, auction houses, etc). The best part of the online aspect? It's free right out of the box.
A more devout player can choose to pay $9.99 a month and with this fee they'll receive more storage space, more character slots, and access to the new content the developers will be feeding into the game on a steady basis. You don't ALWAYS have to pay, but if you're loving the game it'd be silly not to pony up 10 bucks for the new content when it hits.
Anyway, I'll stop here before I go into detail over things that are covered by the NDA. Just take it from me, as a gamer with little shooter skills, that the game's a blast. If you're a fan of Diablo, Sacred, Titan Quest, and all those Roguelikes, you'll want to check this one out. It's a fantastic step forward for the genre, and with any luck it'll be a huge success so we can see plenty more from Roper and his crew at FSS.
Check out the interview with Big Bill at Level-Up for more info on the game, the studio, and its smaller title that could, Mythos.