Amazing how good this game is. Classic Doom, yes the locked room kill everything may be irritating but it is done very well. Secrets are not too hard to find, I can usually find half fairly easily, and Youtube the rest, although you don't really need to find anything in a playthrough, finding around 60% is more than enough to enjoy the game. Those cute little Doomguys are hilarious too, as is finding classic Doom levels. Very very impressed this really is a modern Doom - its basically if the 1993 version was never made this would be a similar classic - it really is that good. The only downside is the stupid size - 55GB download and around 60GB installed. Took near 14 hours to download which is roughly how long the game runs for; there are 13 levels (heh) and each will take around an 1hr to explore more or less decently. Don't forget that the initial levels have weapons as secrets including the plasma gun and super shotgun.
As to the guns, the heavy machine gun is useless, the chaingun is vastly superior and I strongly strongly recommend you at least find the Argent upgrades in each level; your suit can be upgraded to Level 5 for Health, Armor, and Ammo, so your health/armor maxxxed out is around 200 as opposed to 100 or less than 100 and you will run out of ammo less. Also use the chainsaw on lower level demons as you will get piles of ammo. Playing on maximum easy for enjoyment and the lore is also well done - its interesting to see UAC has turned into a cult - employees are expected to live, breathe, and if required die with a smile for UAC.
Very impressed, a 2K16 highlight for me. Actually better than what Mankind Divided turned out.