What a great map. 

It really is as big and monster packed as it promises. Strong theme, strong detailing, reasonably varied, some impressive structures outside. Gameplay inside is consistently good - tough, a bit hectic, but generally fair and balanced. However, gameplay outside, the way I popped into it, was bloody hard and relentless and I got through it by the skin of my teeth - felt like it could have been really frustrating and needed some beefier supplies before popping out. Also having "done" the outside bit, it would have been nice to have shortcuts opening up.

https://www.twitch.tv/videos/420905140 demo from about, errr, 20 mins or so here. More tomorrow maybe. 

Mapping for Quake 1 is something I just picked up recently to try it out

spunks out a 8192^3, 1000-monster facemelter that would make Tronyn look at it and think "hmmm i'd probably have toned it down a bit" 

It's like Telefragged and Warpspasm had a hideous bastard offspring that outgrew both of them.

70 minutes for a 100%, no-one fucking listen to him. It took me 2:30 hours just to get through it, albeit with a bit of backtracking.

Protips:
1. Play slowly and carefully with a lot of duck and shoot.
2. Don't run amok in any areas unless forced to.
3. See 1.
4. Don't try power-up runs as it forces you to rum amok.
5. See 1.

Then it's probably a whole lot of fun. For me there was a lot of fun but a fair bit of frustration on some areas. Overall the sheer INTRIGUE of it kept me going, it really is an experience, like it's thematic ancestors. Congrats Mazu, it might be a bit rough around a few edges but it is an epic release and a must play.

https://www.twitch.tv/videos/421323796 2nd part here. 

Where is it rough around the edges? I thought the map was refined and highly polished. 

Gameplay balance is all over the place, some of it is fine, some areas like the outside bit (madness) and the labs (one health pack for 50 monsters) are not.
Underwater section is too long-winded and frustrating.
Outside section has cool designs but looks like they were sorta dumped there.
Over-reliance on crates.
Quite a few bits of scenery and slime that are awkward and easy to get stuck on / fall into.
Even with the arrows it's pretty maze-like in places.
Shortcuts to previously visited areas take ages to unlock esp. outside area.
Detailing can seem a bit cluttered / arbitrary in places.
Lighting is a bit flat throughout, esp in outside area which doesn't use skybox light.

Please note that these are semi-nit-picky criticisms, but since you did ask. And in Mazu's own words: "my brushwork + detailing is almost whatever quality and all over the place. " - tbh it's a lot better than he says it is and getting any kind of refinement and polish on a map like this is some feat. 

Thanks for clarifying. I thought the outside area was awesome, good challenge (playing on normal) and a good change of pace. Nice visual variation but still consistent with the overall theme of the map. Plenty of ammo if you jump around a bit and find a couple of secrets. The lack of skybox light I thought was deliberate to set the scene of an eerie scrap yard with some serious shit about to go down. The labs were again challenging but with ample space to move around. I thought the secrets were expertly placed throughout the map to balance gameplay. Underwater sections were awesome, rather than frustrating I would describe them as challenging if you fancy a bit of that in a Quake map. No complaints about overuse of crates or slime sections either. Lighting I thought was well above average with sensible use of coloured lights and fog. The map kept reminding me of AD quality throughout and I didn't find anything I didn't like during my first run. As you say, refining a map of this magnitude is a tall order and I thought he did an exceptional job with it. 

Time: 184:14
Secrets 21/37
Kills: 858/925
Skill 3

Spoilers: Don't read this if you haven't played it.

I wasn't a huge fan of the map early on - felt crampy and easy to get stuck on stuff while enemy weapon roulette (guess what colour that silhouette of an enforcer is at the end of the corridor) blasted you from afar. The grenade ricochet off wall detail annoyed me more than it should have, but maybe I'm just rusty.

Once the level began to open up, give more weapons and space and more obviously different monster variety it got a lot more fun. The early play was attrition skirmishing, which is best when the player feels like they have a choice in how to approach each fight.

The five secrets actually as critical path thing was a great way to present the story through the level, especially with the exit fakeout.

I think there are a lot of approaches to this map, given the nonlinear routes and amount of weapons either hidden in secrets or just off the critical path. It's quite easy to start running out of ammo only to realise you missed a weapon pickup.

Secrets were usually logically placed and rewarded the player with more map (always the best reward) although in the early DBS secret I totally missed the weapon at first and only noticed after going back out. The book of loneliness I had to rocket push to.

Overall, and as others have commented, mostly good, sometimes great and occasionally annoying and/or awesome in equal measure.