I'll join as well, even if I've already played an older beta.
I play on Ultra-Violence skill with PrBoom 2.5.0, default compatibility level set to 9, and I play each level from scratch ( Pistol start ).
01 - Excavation Site by Matt534Dog
Short and cool opening level. Thanks to some of the traps ( surprise HK, Shotgunners teleported behind your back ), it manages to be quite hard for a first map, even with a reduced number of monsters.
5 secrets, that's quite high compared to the size of the map, but they're easily found.
( Minor nitpick, for the entire megawad : I like to have the map number displayed on the automap, so that I don't waste time when IDCLEVing. But you probably needed extra character space for your map names I suppose ? )
02 - Research Facility by Matt534Dog
Interesting map with a dark atmosphere.
In the starting area, the player can pick the second green armor ( Thing 116 ) from below, by sticking to the wall. I'd put that armor further away, so that the player wouldn't pick it by accident while going backwards / fighting monsters in the starting area etc. ( as it would then be a waste of the first armor ).
Rather than teleporting the player in the middle of hitscanners after crossing a random linedef, I believe it's best to reveal / teleport enemies themselves ( just like you did later on with the trap just before the Red keycard ).
It's easy to pick the secret Supercharge without stepping on the secret-tagged sector. Maybe you should tag another sector instead ( the entrance of the whole area ) ? UV Max demos would probably benefit from such a change.
Overall, that's a cool map. Maybe there was a bit too much ammo ( Bullets, most notably ).
By map 02, most of the monster cast have already been introduced, including Barons & PEs. This wad is going to be hard. :)
03 - Flooded Caverns by Matt534Dog
Ah, yeah I remember I liked this one, but also that I had a few ammo shortages by the Blue keycard. I see this isn't the case anymore. :)
Music is particularly good here, with some kind of a Castlevania vibe that I happen to like very much.
The dark cave made for pretty interesting fights ( despite the size of the cave itself ), most notably when the Cacodemon group is out. When playing this map in Pistol Start, though, one has to skip them to go and grab a Chaingun, otherwise it would be too tedious emptying your 200 Bullets on them with the Pistol.
Overall, these 3 maps were good, with a nicely-done gloomy atmosphere and solid sense of progression. If I were to nitpick, I'd say that maybe the maps are a bit too linear for now, but we'll see what comes next.