So, I'm going to use the powers of Hell for necromancy, resurrect this thread, and yammer on about how I've started playing Doom 4 (calling it that for ease of reference), and how it scales up. Because as we all know, my opinion is sacrosanct. ^_^
So, having started to play it, it's...well, it's fun. Fun in an interesting way, because I've effectively had to retrain myself on how to play it. Little iron sights, focus on movement rather than cover, no regenerating health, etc. I'm not saying that these things are inherently bad, but it's very much a case of an old gameplay style being modernized. That said, it does get a bit samey, how it's effectively one arena after the next. Very fun arenas, but it's different from Doom 1/2, where monsters are around and about and you can tackle them at your leisure. Also, it's far less linear than, say, Doom 3, but not as open as Doom 1/2. As others have pointed out, it's not so much a Doom remake, but rather tapping into what one thinks of Doom and modernizing it. For the most part, it's a middleground that works, but I have found myself bored a few times. Doom 3 kept me immersed about 90% of the time - this is more 80%.
Also, the story. I know this will be completely academic to some people, but the story of Doom 4 is...well, weird. Mainly in tone. Half of the time is spent establishing how and why the UAC is on Mars, the other half is ARGENT ENERGY! Half of the time it builds up a believable 22nd century setting (e.g. VEGA and the application of the Turing Test), the other half it's winking at the camera, saying "the UAC is a cult, laugh at it!" When Doomguy destroys the Argent coils, half of me is snickering, thinking "heh, he really doesn't give a damn about what Hayden has to say." Yet I'm also thinking "well, this guy's an arsehole." Hell has to be defeated, sure, but Earth relies on ARGENT ENERGY! and he either doesn't realize that, or doesn't care that he might well be dooming humanity anyway. It's like this weird middleground between Doom 1 and Doom 3, and I feel Olivia Pierce is the poster child of that. Now, Betruger was pretty much guaranteed to be the bad guy from the start, but you could at least guess about Swann and Kelly, as to whether they were on the level or not. Pierce though, is outright evil. I realize I'm not that far into the game, but, yeah. Like I said, like the gameplay, the story is a weird half measure between Doom 1's borderline contempt for narrative, and Doom 3's attempt at hard sci-fi mixed with the supernatural.
So, anyway, current ranking is probably D3>D4>D1>D2 for me. I could see it switching places with Doom 1 on that scale though, but at the least, despite my gripes, I'm still enjoying it.