Well, I only downloaded it this morning and have only had the chance to play through the first 3 levels. All in all, I really like it. It has the feel of the Doom alphas (a lot of blue and a fair few 'plain' textures) mixed with something new. Sometimes there's almost a Demon Eclipse atmosphere and some of the sprites and textures fuel that atmosphere. On paper it sounds like that juxtaposition wouldn't work. Something so old feeling with something very new but in actuality the both marry well together to create something quite fresh. The new monsters work well and don't feel extraneous in any way. In fast, they make you think about how you play and force you to change your 'standard' tactics which is a good thing!
I would, however, point out a couple of things (of course!). The music in level 2 (Wicked Flowers) doesn't loop properly and stops for a good while before starting again. I've seen this in a couple of WADs in the past so I'm unsure if that's a ZDoom limitation or a flaw in the music itself... The other thing I would comment upon is the sprite for the Plasma Shotgun. I don't think it fits too well with the rest of the weapon set. All other weapons are centre-based whereas the Plasma Shotgun is biased to the right. It was quite jarring when I first picked it up.
Other than that, so far, it's been really enjoyable and I'm looking forward to playing through the rest of it after work tonight. If you want any more feedback I'd be happy to share.