There was one thing I was wondering about, though. Does the glass orb in the end of the final level ever go down? I fired every single shot I had at the orb, used the B+A+T cheat a few times to get extra ammo (the only time I ever used cheats in this mod), and the orb is still there. I even looked elsewhere in the level in order to see if anything changed (and nothing did, if anyone was wondering). I'm not sure if I accidentally triggered a bug that made the glass orb unbreakable or it just requires so much shots. I have saved in the level, so if you're interested in taking a look at my save file, Gridlock, then I could give it to you.
Ugh, this is unfortunately a bug that I was hoping people wouldn't run into. For some reason, on a small percentage of attempts, the QED patch fails to trigger its final explosion even when its health has been depleted. I'm assuming that the orb was pretty cracked at the end, even though it didn't get destroyed, right? So far, Levellass hasn't figured this one out yet. Hopefully, it can be fixed in a future version.
If you send me the savegame, I can try to work out a solution and send you a new savegame. Otherwise, some things you can try (enable cheats with A+2+Enter):
a) Die, restart the level, and use cheats to get back to the top of the level. See if the QED fuse responds to shots. I've found that sometimes it'll break on the first shot, other times it'll still be glitched and won't take damage at all, and other times it'll behave normally.
b) Use warp cheat by pressing F10+W (the text will be corrupted due to patching), then type the number 12 and hit enter. You'll be back in the level. Try destroying the fuse again.
So sorry about that

. Let me know if works. I promise there is a real, big ending.
I might be inclined to have them a bit shorter, but I don't know if you intended the levels to be played with ILS, so if you did, they're balanced perfectly fine
In-level saving is definitely recommended, though of course people are welcome to try making it through these levels on one go. The inability to include checkpoints in standard Keen 5 is an unfortunate limitation.
Also, I just now realized while glancing over the levels in the editor that the Extraction Core -- or X-traction Core -- is a giant X. Hehe

This is the only level that I would like to see adjusted a bit. It seemed to have more repetition and backtracking than the others.
I'll take a look at improvements for the next version. Also yep about the X
Unrelatedly, just because I'm curious: is there a meaning to the defense tunnel names?
Maybe a small easter egg (I'm surprised you didn't notice it)
I don't have a lot to say about it, but, I liked the Mars base detour. I almost wonder if the Koraths could have been visually replaced by Yorps, but maybe that would be too much of a change for this style of mod. (I was never sure what the relation between the Koraths and Shikadi was anyway... it's strangely vague.)
Ha, I thought about changing them to yorps. Though, I couldn't think of a decent explanation of how exactly yorps ended up on the station above Mars, so it was just easier to go with the Scotties again

. Agree that there's not a lot of lore to go on with the Korath.
According to the wiki, I guess there's a bonus stage, but I didn't find it - maybe I will have to look later...
(although I seemed to have missed the secret level, assuming there's one since KeenWiki stated there's one)
The wiki is wrong and will need to be updated. There is not a secret level (Mars Station is required), and only Ventilation Ducts is optional. Of course, that's not to say there isn't at least one big secret that hasn't been found in the game yet
I have to wonder... Why no Spirogrips? I'm not complaining by any means, though. I abhorred those things as a kid (not quite so much now).
I'm not a fan of them either. The main reason, though, is that the spirogrip's frames were recycled to create the QED sprites at the end of the game, so it's not even possible to put a spirogrip in anymore.
Keen's face looks kinda weird in the title graphic, but I get where you were going with it.
Eh, yeah, would be open to improvements if anyone has ideas.
I also found this, though. I'm not sure if it's a memory error or something, but, in this one big stage toward the end, I was in the tunnel (right pic) and suddenly Keen started being rendered on top of absolutely everything, including the foreground.
This is another weird bug that eludes me. That's the first time I've heard of it popping up in Dynamo Guard Vault... the only other place I've seen it is the west defense tunnel. I have no idea what causes it.
Thanks for the feedback!