I never had a device before that I really wanted to be playing games on, so I never spent a lot of time with Doom's previous flavors -- this one is an RPG variant on the classic Doom shooting gameplay, made just for the iPhone by Id. Right now I'm really digging it, and for me it's worth the time spent because I'll have my phone awhile still. There's been thought and effort put into the controls of this one, and you can tell it's a game designed to play on the iPhone.
Releases like this and the continuing efforts to port old-school games forward to the current generation of hardware have been going on for years. I think it's been going on long enough that people are less interested in doing it for the cred and more because these games are genuinely fun to play. Unless someone makes a better suggestion in the comments, once I conquer Doom II RPG I'll be (not so) patiently waiting for the iPhone port of Riven. (Ed: Don't tell Kelly, but that's out, too!)