Level 1:
-Same issues with the waterslide, if you simply jump towards the end of the slide, you can go right through it, or if you use the jet or jump diferently, you can walk on top.
-I saw a enemy spawn below the ground (the black sphere was half sticking out of the ground), and then the enemy came after me, emerging from the ground
-I think my problems with the cart happened because I was to impatient, there is a slight pause (the engine revs first) and then you can move forward so for a good 2 seconds the controls are unresponsive, so I don't think there is a problem here.
-The issues with lag, (at least for the rar files) where due to my computer yesterday acting up, it runs fine now, no lag at all.
-On a hunch, i tried and confirmed my suspicions, if you do anything in the main level (outside) like get the cart, or get the jetpack, or destroy the gates (and if you have 100 guys after you, but this can be skipped) once you enter the converted barn and come back out, it is as if you restarted the level, no jetpack, no cart, no destroyed gates, and you have to do it over agian.
-I wasn't origionally going to mention this because I think it is trivial, but I will since I'm doing everything else, the 3 messeges for the cart once you get closer and closer, if you move fast enough commonly get mushed together so you can't understand her.
Level 2:
-I realized the issue for the UFO's not being seen until you go back towards the hanger, this isn't because they arn't spawning, but actually, I kept turning around this time to look for them, they were all spawning behind me while I walked/ran to get the key, when I came back, they were all waiting for me.
-You can still get stuck on the lights in the cave.
-This is an overall problem, don't you pause the game when the person does the menu key? I can still hear the UFO's moving and shooting while I'm in the menu, and I think I ending up dying while in the menu.
-When I was dead (I'm in a menu and there is no save present) I can still hear myself moving, UFO's shooting, and I can shoot, and I'm sure if I was near a level change point, I could probably change levels as well. It would be nice if I had a start from begining of this level button, the only save I had was at the end of the last level, I have to restart now lol.
-Same performance besides that, I am noticing a tiny bit of lag though, are you making entities visible (like the rocks) as I get closer and disapearing when I'm farther? if your not there is a posibility to remove a little lag (its barely noticable though
Level 3:
-Same thing
Level 4:
-I'm pretty sure that bullets are going through the asteriod sometimes, you might wanna check how many frames there is between each check of collision and change that ammount
-The reason I'm rather sure the bullets go through the asteriod is because when I fired at one, and apprantly missed, the asteriod went through cockpit, towards me, through the glasss about 5 feet and then vanished, and made the standard damage and sound of collision
-The game still crashes here at the minigame but not seemingly as frequently, it took me 2 times before I got through this time without crashing
-The loading code might want to be checked on, it crashed once when loading a save file.
-I spammed the flushing toliets and after like 10 tries they stopped flushing (all of them), was this supposed to happen?
-One last error I didn't mention earlier but I'll illistrate it in the picture below cause it does deserve to be brought to your attention at least.

Level 5:
-Same, didn't crash either time like it did in the first installer though, but I did do this one rather quickly to be fair
Level 6:
-I took the trolly for the first time all the way through, it was kinda fun shooting rather than running, but I went THROUGH two of the UFO's on my little ride
-I noticed when transitioning levels you regain all health, if you want to make the game a little harder, you could keep the same health from level to level. Otherwise you might be able to run back and forth between levels whenever you get in trouble.
Level 7:
-Same, I could same something about it telling you about you have to find a key even if you have one, but that is kinda irrelevant
Level 8:
-I stuck around in this level for a while to make sure if it crashes like the previous installer would, and it did crash every now and again (after like a minute or so)
-Besides that, same, oh one more thing, I'm not sure if I mentioned this before but you might want to let the player know he should check for a door for the key in a previous area, I was a little caught up in this level the first time I did this before I realized I had to go back. (Just say something like "Hey! A key, I bet this goes to a door we've already seen.", the garden is a little specific so don't mention it, you want to guide...not force a player to be someplace, I personally had no idea I was looking for a key, but since that's what I have been collecting this whole time, I felt satisified that I got everything once I found it)
Level 9:
-Found another glitch, I hopped on the elevator rail just to be goofy when it was moving down to level 9, hopped a couple times and then got lodged in the wall and I traveled (unwillingly) up the wall and into the ceiling of the garden level, I repeated this again (on purpose this time) all you need to do is jump near the wall, you get stuck after a couple tries and if you press a certain movement key you work your way up the wall, but you can become unstuck by wiggeling a bit.
-Back to the reactor, I'll clock how long it takes before each crash I'll start when the level loads and stop when and if the screen goes black.
The first one is 12 seconds long (Didn't even get in the matenance door), second was 37 seconds (just unlocked the control panel to the reactor), 41 seconds I was jumping for the panel, 43 seconds (same as last), 11 seconds didn't make the door, 36 seconds almost to jump point, 38 seconds about to jump, 22 seconds just at the stairs going up
P.S. I have a really large hunch that the crashing revolves around your enemies code because whenever there isn't a bunch of them (aka the garden and the first level, and to some extent the 2nd and 3rd levels as well), but the really compact levels with all the enemies seems to crash the game all the time (aka the last level after a couple of tries and definately the 9th level). This is just a hunch though, they could be completely unrelated for all I know
Sorry guys I can't test anymore I have school work to do now, maybe a bit later I can help,