Finished the game this morning. Brilliant, simply brilliant! It took a couple of levels for the slightly different approach of combat to click with me (I was hoarding the chainsaw before hand, but when I understood just how plentiful everything is, my mindset changed and I improved as a result). Personally, I probably enjoyed this more than the last game - the way you use certain weapons to weaken enemies quicker is just something that I loved and once I memorised all the enemies weaknesses I was switching out weapons super quick and destroying hoards of demons no problem! All the mechanics you are given to dispatch demons (including the flame belch and grenades etc.) all just mesh together almost perfectly. Sure I'd get stuck on the environment at points, and the first couple of levels are probably less fun before you get your whole weapon set, but speed running those levels for later at least makes them more fun on the replay.
As for enemy variety - I loved how they managed to rep the cast of Doom 1&2 whilst including a few new enemies. I loved the fact that Kakodemons are closer to their original Doom look, and personally speaking after learning how to tackle the Marauder I quite enjoyed fighting him as well.
Boss wise, wasn't a fan of the Gladiator (felt like he homed in on you way too much), loved Maykr's fight (once I got the rhythm of the fight down it went pretty smooth) and my only issues with the Icon are that right at the end it spawned an insane amount of enemies (and I'd used all my BFG ammo) and it was a bit tough at times to tell which bits needed to be shot to further damage the boss.
But all in all, its excellent. The Doom reboot and Eternal are probably my favourite two FPS games this gen, only TF2's campaign comes close. Also, I was impressed by how well the performance on the game held up especially at the end with all that shit on screen and with it running as fast and smooth as it did. Easily my second favourite game of the year (Yakuza 7 is still tog dog)