Unfortunately, I don't have enough time and endurance to review your whole pack, but I did want to give you some pieces of advice. First off, this pack really shows your (quite rapid) progression as a mapper. While the first map is quite a typical throwaway first attempt, the last map in this pack is quite an impressive showcase of ideas and mapping knowledge that simply lacks in organization.
For being so relatively new to our community in general and level making specifically, you know quite a lot about mapping specials and the likes, probably much more than many people did at this point in time. Also important is that you have inspiration. It's not like your maps are empty shells of nothing (again, excluding the first two maps) but instead, you have many interesting and sometimes quite complicated gameplay ideas that make your maps enjoyable. Of course, with the success comes the failure, as some of your ideas simply fall flat on their face. That is entirely normal, it took me personally over a year before I finally had a good understanding of what works and what doesn't in this game.
For example, there is this section in Jungle Flight where you have to choose between two springs. One leads into the pit and one lets you progress. This doesn't work at all, since it's more or less a matter of luck if you survive or not. Apart from that, bouncing off long spring chains is not very interesting, since the player doesn't to do much.
Another example can be found in Toxic Adventure where I have to press several buttons after another to open a door. To make it even worse, I have to run back and forth between the two sides of the room, which is extremely tedious and boring. In general, having to press a button to make something happen always feels kind of lame and uninspired. Try to think of alternate ways to make certain events happen (though I loved the idea with the oil barrel button, hands down).
One thing that needs drastic improvement is the texturing, and the visuals in general. That is a particularly tricky field for new designers, I have to admit, and I'm also very picky in that matter. Simply put, there are many spots where the texture feel like they were randomly pasted onto the walls, just to have a texture there. Making a level look good is a tricky thing, and requires trying many things out. I would recommend starting with some preset themes, and not trying to experiment all too much. Also, you don't seem to know about texture alignment, and I blame the stupid SRB2 Doom Builder Tutorial on the Wiki for that.
See, now I've written much more than I planned to, but eh... In general, just continue trying out things and looking at what works and what doesn't, it's probably the best way to become a better mapper. Also, play as many custom maps as possible and look at what you liked there and what you didn't. Slowly but steadily, you will get an impression of what is good design and what isn't.
(Slightly offtopic: The fact that Metal96 liked those spring chains really shows in his own level, and not for the better. But that is another review...)