At first, I was skeptical based on the DOOM mp beta, but now I am still surprised at how well they did with DOOM. I can see them riding their success with DOOM really damn far.
I can easily see them pulling off a new Quake single player game and a great multiplayer portion as well. Imagine a new Quake game? A good old fashioned single player Quake?!
If they have the rights to Duke Nukem or if they can get them, I can see a badass and proper Duke Nukem coming from these guys as well. If they did this good of a job with DOOM, I have full confidence that they can breathe life back into all of those classic titles. I can see a new Quake arena MP game kicking ass with these guys at the wheel.
I thought the glory kills would be a mundane distraction that I wouldn't ever bother to use, but they are actually an integral part of the game and I enjoy using them. They are creative and satisfying to use. Ripping off a demon's horn and jabbing it in it's eye? That's badass. They made sure it was badass. And it is badass.
And yes, the game runs awesome on lots of hardware. People can play this game. You don't have to spend some seriously twisted, evil amounts of money to get a great experience from this game and have it look awesome at the same time.