Welcome! I hope you don't mind that I moved your thread to "Beyond Jazz Jackrabbit 2," which is the forum for fangames and such.

I tried out your game here and had a good time, it felt like going through a SAGE game with more rabbits in it

Things I liked:

• There's a lot of custom art everywhere! Based on the themes, I was expecting some classic JJ2 tilesets like Aztec or Building Site or Metropolis, but you did your own thing instead, which does help this feel like its own game and not a JJ2 level pack.
• The falling boss and the wall of saws are good platformer tropes that don't appear in the normal Jazz games, great job adding them to the lineup.
• Speaking of standard platformer things that don't appear in the normal Jazz games, pressing down to fall through platforms! Whoa!
• The enemy edits were cute!
• Having the unused door sprites for the bonus warps was a neat touch
• Always neat to get to fight four new bosses, even if the third one was pretty simple and the second suffered from a difficult camera.
• The new HUD was a cool touch! Having higher resolution portraits for the weapons makes a lot of sense--they're easy to miss in JJ2--and I love the upset Jazz head when your health is low. (Score is very prominent for how useless it is, though.)
• There was clearly a lot of work put into the menu presentation, especially Spaz's chalkboard sequences with all the great doodles.
• I've played so many indie games without keyboard customization menus, and yours works perfectly!

Things I was iffier about:

• For all that there's a lot of new art and that's cool, it's not really a coherent art style. The backgrounds have much bigger pixels than the sprites and walls, in particular, and the hearts seemed like a less attractive alternative to JJ2's. Almost all the enemies are JJ2 styled, except the JJ1 turtles.
• This is a tough one, because I recognize it also describes JJ1 and JJ2, but: lots of enemies just walk back and forth. It meant that I hardly ever really needed the weapons, I just tried to use them because it would feel like a bummer not using them.
• Speaking of the weapons, I liked the laser (though it didn't do too much damage, so it was only useful in the rare cases with multiple enemies), but too many of them are just a single sprite moving left or right. The ricochet gun is cool in Jazz Advance because you can bounce it off of slopes at 90-degree angles, but here it's barely distinct from the basic blaster.
• Wish I could have seen how many coins I had, though the secrets were obscure enough that I only ever got into one bonus door.
• Both JJ1 and JJ2 let you change weapons by pressing the number keys on the keyboard, and I found myself missing that function constantly.
• The moving platforms were tiny (and not very attractive). It also feels like there should be at least one platform that moves in a circle, both JJ1 and JJ2 love that.

Things that seemed like bugs:

• The springs were the wrong colors. Red is supposed to be the weakest, blue the strongest. Both JJ1 and JJ2 are consistent about this and it's really offputting having them the other way round.
• The springs just seemed buggy in general. Sometimes I could stand in front of them. Sometimes after using a spring, I could jump in midair, probably because the game still thought I was standing.
• When I froze an enemy and let it unfreeze, it would take a couple seconds to start animating after it started moving.

Overall I think this was a perfectly playable little game--as you say, simplified from JJ2, just a quick little adventure--and a really pleasant surprise. There could be some more polish in some areas, especially the clashing art, but it's very impressive for a a few months' work. It's a lot more platforming-oriented than the original games, but takes advantage of the resolution to put in a lot of enemies and goodies.