Finally got to play this today, on Nigthmare. Quick thoughts:
Either the engine is pretty good or the game has a fantastic optimization (maybe both) has I can run it with max settings with an average of 120fps (I have a mid-range desktop). Plus now that they ditched the megatextures game occupies far less than D16.
The ammo capacity has indeed been considerably lowered, but specifically for the shotgun. In the first level I ran out of ammo very fast, which forced me to chainsaw someone/look for ammo constantly and that pissed me the fuck off. But again it's mostly the shotgun. Once I got the first ammo upgrade the machingun had a confortable amount and once I found the plasma rifle the game never once again had that problem that kept fucking up the flow of the battles. By the 2nd ammo upgrade the shotgun actually lasts.
I've reached the super shotgun and stopped playing after the first arena with it. The weapons so far are an improvement (for the most part).
The shotgun has a smaller range than D16, but the weapon mods make up for it, and while the way the enemy's weakness are set-up it favors much more the grenade attachment but the auto shotgun is super fun to use.
The plasma rifle seems to have been the weapon that got the best overall, in this game I actually enjoy using it. It does a good amount of damage, it's attachments are better than ever and it just looks and feels great to use. It's super useful to sweep the levels.
The rocket launcher is the same.
The Super Shotgun also has a smaller reach and spread but it's damage seems sigthly higher than the base super shotgun of D16 but much lower than the uranium coating upgrade. The meathook is pretty fun to use and allows for cool movement.
The machine gun however... the upgrades are the same but now the scope is actually useful because of the weakspots. But the weapon itself is worse than it's previous iteration. It does poor damage and the it's new sound fx is equally weak and embarassing.
The chainsaw can be used from a ridicolous distance. Seriously you can instantly cut down an enemy that's around 10 meters away. Plus now it auto refeals 1 bar, it's obvious why they did this, it's because the enemy count is much higher than D16.
The flamethower is more useful than it first seems but I keep forgetting to use it. Being able to throw a grenade without having to stop shooting is useful and so is the ice grenade.
The melee attacks now does no damage unless it's a blood punch. That's a stupid modification.
I am pleased with the challenge Nigthmare offers.
The enemies are more agressive than ever and now even the zombies can be a problem, given that now they carry flamethowers and plasma rifles.
I feared the enemy weakspots would make the combat too mechanical, but so far that doesn't seem to be the case. It's a neat mechanic, the only enemy I would say the failed are the Cacodemons, it's too easy to pull of and the "reward" is massive (immediately becomes staggered). They should made the conditions more difficult to pull off (for example: he can only swallow a grenade during attack animations; or you have to deal X damage to the eye) plus made the payoff not as broken (the cocademon can no longer use the fireballs).
The levels are IMO pretty chunky, considering I am half-way the 3rd level after playing the game for the afternoon.
There's actual optional content in them, and I've seem some challenges that I am sure where designed with a late game arsenal in mind, so they much more replayable than D16.
Also I am quite liking the location variety and how much more fun the arenas are.
There was an encounter on the second level, near a giant mech slaying a demon, that had 3 arachnatrons, and boy has that though.
I noticed some invisble walls specially on the 2nd level, where I could spot some areas of the level below my current but the game would "kill me" if I tried to jump. This is obviously artificial and hurts exploration and speedrunning.
The game has faster pace than D16, since there's more enemies, they are more mobile and agressive, the player has more movement related abilities and the movement speed seems sightly higher.
Well it's being more fun than the best levels of D16, so I'll see how the game progresses.
