After I spotted 0.8-beta and the call for testing, I gave Freedoom another playthrough and I have these remarks about the levels. I use Debian's prboom 2.5.0 and played on difficulty 'Bring on the Pain'.
*Spoiler alert* in case someone cares.
*Map05: I accidentally opened the switch at (x=-468,y=269), but I don't know how. Does it have multiple triggers?
*Map09: got stuck near the birthday cake (2510,2783).
*Map10: is obviously not finished, but for what it's worth there's a missing wall at (-4261,529).
*Map11: there's an unreachable secret at about (2577,-431), different from the secret room right next to it. The secret at the end containing the yellow skeleton key is quite evil to trigger, is that OK?
*Map12: the top of the rail at (2394,4426) is missing a texture to close it. That last part of the level seems a bit unfinished, with an apparently useless piece of machinery near that rail and other not-quite-finished ideas.
*Map14 has an invisible column at (1085,-3081) and offers a peek into an unused corridor at (1263,-2449). Also the timing of the door to the not-secret room is quite evil, I couldn't get in after several tries.
*Map15 displays glitches at (1075,-559) and the other lattices.
*Map20 has similar glitches under the bridge at (-1740,1429) and the balcony at (3375,-1486) shows no floor.
*Map23 has an unreachable room with a secret (-588,4198) and other stuff.
*Map24 contains two enemies that didn't spawn, they're kept at (1094,-1161). And how do I open the secret at (367,-490)?
*Map25 has a large unused area, and also three coward monsters around (1239,999).
*Map27 got me stuck at (927,4386), I fell between the crates and the wall. It also has an unreachable exit at the north edge of the centre court (-438,3507). How do I open the pillar at (-84,-152)?
*Map28 shows a narrow glitch at (221,1334).
*Map30 glitches when you reopen the door at (-2248,1609) after you went through.
*I sometimes underestimate the monsters' bounding box, thinking I can get past them but being blocked anyhow. Is that an engine limitation or does Freedoom have narrow sprites?
*The demo player kinda sucks. Is that a feature or a bug?
*The 'blue armor' is actually red.
*As I'm no native English speaker, I'm not very sure but I think there's too many hyphens in the text. E.g. Extreme-carnage, slither-beast, mini-gun.
*An idea for better integration between the levels: provide consistency in which floor types are damaging and which are not (lava, blood, biohazard, ...). The sight of the ooze in map14 made me reluctant to jump into it, remembering map05, but apparently this one was harmless. Also: some levels start with immediate action, which I find a bit annoying as it leaves me no chance to save the game quietly.
*Last question: are the 'Freedoom I' levels released as a WAD? At any rate they don't seem to be included in the Debian package.
Overall, I agree that the levels vary in quality and difficulty, but I certainly enjoyed Freedoom. Thank you for it!