Just beaten this, thoughts below:
+Does the core elements of a FPS well i.e. weapons, monsters etc
+Guns feel suitably meaty, i.e. double-barrelled *BANG*, have some of that. The first time I knocked back a Hell Knight I smiled and thought yeah, you nailed how this gun should feel.
+Acceptable game length
+Good graphics
+Acceptable performance considering I'm using a mid-range card from 2012, most of the time it runs around 70-110fps with drops as low as 40 in the worst places (probably about 4 occasions in the game where it was becoming noticeably less smooth).
+Reward system is generally good, it's nice upgrading weapons etc
+Auto-map makes a welcome return, I always felt it a shame that something we had back in era of DOS gaming had kind of been done away with
+Bit more of a fun/arcade focus on than Doom3, not much in the way of dark corridors and shock scares etc
+Proper boss fights that let you make sure of the arsenal of weaponry you have saved up rather than some stupid gimmick involving switches or whatever, they even got the balance right in that like Doom, the Cyberdemon is actually tougher than the final Spider Mastermind boss (I think I needed about half a dozen attempts on the CD whereas SM went down first time)
-Performance doesn't seem very scalable with options, i.e. I don't really gain much framerate dropping several settings from High to Low
-Can't set weapon priority for auto-switch, it seems to favour shotgun over super shotgun, machine gun over minigun etc which is annoying
-Chainsaw seems OP/simplistic, basically a no-skill instant kill weapon rather than you having to wield it yourself. I probably used it maybe 10 times in total (normally I forgot about it, could have been useful against pinkies etc)
-Few annoying occasions where if you progress too far into a level you can't go back for collectibles etc as the way back is blocked, this is annoying when playing the game for the first time because you don't know if you are actually near the exit and should turn back, or if you will be returning near to an area again (dependent on whether the level progression is linear or cyclical etc)
-Bit of a slow start, it isn't really until Argent Tower that you actually get a decent number of monsters coming your way at once
-Default ammo capacity is a bit low for my liking, you can only get 10 shots out of the SSG for example. I know you can upgrade it but to me that was really just dealing with an annoyance, I wanted to spent my argent cells on health and armour first as I figured that would give me the best chance of success (kinda felt like ammo would be wasted given I never run out of ammo for all weapons).
-Outdoor level design a bit poor at times, a few too many ramps and a couple of places where you should be able to climb up but are blocked from doing so
-I'd agree with the comment about about level pacing, i.e. it is a series of discrete battles rather than one seamless level so you can't charge around orchestrating a fight with 30+ monsters like you can in Doom2. Probably a byproduct of the checkpoint system
Overall this is a good game and kind of felt like a reboot should to me; it borrows heavily on the Doom lore and retains some key design elements, but re-imagines it in better environments, slightly enhanced monsters, slicker experience, better story etc. The fact it has been well received in general is quite re-assuring to me, as I wasn't sure that there still the demand for this sort of traditional FPS (more combat, less cinematics, carry as many guns as you want, not overly focused on 'realism' etc) any more