I'll be interested to see what the secondary "fire" function is for the chainsaw. I noticed the number six in the bottom right corner when it was equipped in the Tech Base demo. Maybe it's nothing, but it looked like a possible ammo counter. The number wasn't dropping during use though.
I've been playing the original Doom games since I was a child in the early 90's, and still play them on a weekly basis to this day. As someone who enjoys Doom that much I have to say that I liked what I saw in the demo videos (four times each) for the most part. My concerns (enemy design, color palette, level linearity, and speed) have been hit on my many people so I won't beat a dead horse. Despite those reservations I'm still excited for this. So few of these style of FPS have been released since the 90's that I'll salivate over any of them, let alone a Doom game.
I do hope they tune up the shotgun a bit more. It's range seems to be piss poor compared to what it used to be in the originals. There needs to be a use for the shotgun that makes it viable throughout the game, and different enough from the SSG that you'll want to use it in different situations. A tighter spread, and higher rate of fire would make it a more versatile weapon while still not making it the only weapon you'd ever equip.
The Heavy Assault Rifle and Chaingun seem to occupy a pretty similar space as well. I'm thinking the HAR's scope and lower rate of fire will make it a better long distance choice. The Chaingun should shred up close, while the HAR is better at picking off enemies at range without resorting to putting a Sniper Rifle or Railgun type weapon into the game. Very, very interested to see how they balance these weapons.
The beauty of Doom to me is it's sense of balance. Switching weapons around regularly to suit the enemy, or group of enemies you're tackling.
Hoping they remove the piss filter, although I doubt they will. Looking at the recolored images makes my heart hurt.