Wow, you're really putting these out! When are you going to start modding? :)
Level01: Superb start to a new map pack! You maintain the two-by-two red feel of the Mars tileset, and you give us a small but well-designed area to get used to your mapping style. I've never been a fan of "do the section over again, now that you have a keycard!" levels, but this one is short and sweet. Great start.
Level02: Good dome level, but the upper left feels barren. Why not distribute some points here, or shape the entire upper ceiling like a dome?
Level03: I have some serious, serious issues with this level. First of all, look at what the player sees, the second the level starts:
That's sensory overload! Let's count: One Red keycard, lower right. One Garg guarding it. One Garg directly beneath the player, in an area accessible to the player's left. Two yellow keydoors, and a single yellow keycard. A ButlerBot, a Yorp, and three Fires. Now, granted, all of these things do not IMMEDIATELY threaten the player, but they are all animated, which gives the level a sense of "everywhere!" which can be alarming.
Not to mention that if the player chooses to go left first, they have to kill themselves. Or if they fall down to the bottom floor without the blue keycard. There's no way back up. (Can you tell my instincts told me to go left first? Look at the screenshot--it's a bigger area... it looks more attractive. Psychology.)
Continuing on in the same level, you do a "drop lined with points" thing, here:
Which drops the player into a fire!
Not cool. As soon as I hit this, I got a little frustrated. :( Last question about this level: What's the deal with this little side area?
There's no reason to go anywhere NEAR that PatPat... I can just pogo up to the pizza from the ledge on the right, drop down for the gun, and hop back up safely.
Level04: Another cute little dome level, and we get our pogo! But I have to ask: What's up with these lolipops?
Level05: There is exactly one dangerous part to this level, and the rest of it is gravy. That's not necessarily bad level design, but I think you're doing yourself a disservice by having the levels so snug. I very rarely say this, but give yourself a little more room to work! :)
Level06: When I played through this one, I thought it was a cute yet simple little side level that should have used the Red Mars two-by-two tiles like the first level... But then I opened it in the editor. Two ship pieces in one location, neither of which is obvious? I don't like it at all. The fact that I had to open this one in the editor to even FIND the ship pieces speaks for itself. :(
Level07: This one is hilarious--it pieces together enough familiar parts of original levels so as to toy with our expectations. I found myself frequently going the wrong way here--but in a good way. :) Nice level. All I would've asked for is the classic Keen1 level border around the edges. Good work!
Level08: *unchanged*
Level09: Big warning sirens go off in my head whenever I see more than one keycard in one location:
I can't think of a single place in the original Keen games that has multiple keygems/cards sitting in a row. If a player has to obtain two keys in one place, you've probably got redundant doors. :)
Level10: In theory, I like this level: Cross a lake, explore an ice maze, find the exit. In practice, the lake is stagnant and dull, and the ice maze is too brief. Again, I feel weird for saying this, but give yourself more space to work with. Variation in the vertical level of the platforms, more headroom in the ice maze... don't cramp yourself!
Level11: So here's where all the extra space went! There's a lot of nothing in this level... which is a shame. From an exploration standpoint, the rewards don't seem valuable enough to warrant the risk (a single teddy bear near those ice cannons versus the same teddy bear for blasting one Garg...) and the blind drops into water really bother me. Nice base idea, again--I really like the way you captured the construction of the Mars environment--but this needed a bit more playtesting.
Level12: I did not find the secret level--I can't comment on it, as I didn't play it. :) It looks tricky, in the editor, but I like the recognizable/familiar sections. Good job on keeping the classic feel.
Level13, 14, 15, 16: *unchanged*
Overall, I have to agree with KeenRush. You did a fantastic job, as in your Keen3 level pack, of capturing the environmental quirks of the episode. You use the two-by-two red Mars blocks in a consistent, recognizable fashion, and you color-code areas reasonably well. My overall criticism is your lack of level borders. Refer back to Keen1's levels and notice the cyan pillars on the left and right sides of the levels, and the long bars over the tops... helps give a concrete edge to the levels.
I'm really excited to see you accomplishing so much with so little level space--I'm definitely a fan of the shorter levels, but I feel that you're stepping on your own toes, here. Your big levels are a hair too big, and your small levels are a tad too small. There's a happy medium there, I can taste it....
...and I hope your mods find that golden balance. ;)