So I took it for a few test runs and here's my after thoughts ^^
First of all I like it a lot more than D4D (at least what I had played of it at the beginning of development) mostly because of droppable upgrades and stuff like that ^^ That's amazing. The gameplay feels smooth and fun and dynamic.
However there are quite a few problems still IMHO to get a full DOOM 4 feel
First of all the running. Part of what makes Doom 4 very fluid is the lack of "stopping" time (or at least almost none). I don't know how doable that is in ZDoom, but reducing the time it takes to sprint to the other side when you've sprinted to one side should be reduced. That time it takes to slow down gets me killed by projectiles so many times (mostly because they're faster than standard Doom, which is fine, the projectiles should be untouched, it's the movement that IMHO is the problem in that case

)
Difficulties : I feel like anything from Normal : Few monsters to Hard : Few monsters are a walk in the park, while anything above transforms into a player slaughterfest. Doom 4 could afford 2-shotting you in nightmare because of mobility, but not that many megawads contain high ceiling maps, and there's always a couple of maps that are low ceiling anyway. That matter could be solved in multiple ways. First adding a middle ground dificulty where I can still use max monster but not be slaughtered to be pieces whenever I decide to hide behind a wall for a sec to escape a projectile would be a great addition (although I do realize creating a full new difficulty is quite some work). Another thing that could be done woudl be to adjust some monsters to the level design of Doom. Maybe reduce the sprinting peed of the pinky, fire rate of the Cacodemon, that kind of stuff. Being 2-shot by a lost-soul with 100 health feels harsh as hell when you know a lot of maps use them as cannon fodder because they are no danger in standard Doom
Also there's one missing feature from DOOM 4 that I feel would be important. Enemies dropping health when in a dangerous situation. That is also one of the reason DOOM 4 can afford being so punitive with damages at time. That probably is one of the easiest feature to implement in the list I did and would probably make Hard a much better experience, with a difficulty leaning toward Doom's nightmare.
So yeah that's mostly my feeling. My main complaint would be that I can't find a satisying difficulty, I jump from too easy to too hard between hard/few monsters and hard/more monsters and anything in normal feels like I could be standing in crowds just waiting for staggering enemies.
Now keep in mind I love the mod and will still probably play it, and it comes from a Doomer than never uses save mid-level (which could be one of the reason I die so much without completing levels)