Where to start?
Firstly, the opening level.
Spawning in a small hallway with a teleport directly in front of you defeats the purpose, when you could've just plain spawned in the room you teleported to.
Also, I like the idea for the strutcure of the litle altar things that you used to teleport, I just wish that they were scenic and you didn't have to travel through them. Next, teh spin tunnel. I'm just sitting, rolling at an incredibly slow speed, waiting for the madness to end. Madness.
And then more temple stuff that really should have been better. SRB2 is about flow, and sadly, a bunch of steps that you have to jump over doesn't constitute as flow. Why? Because you have stop every single time you land before jumping to the next step. Even worse, the flats. I really wish you didn't use special stage flats, and instead chose something along the lines of RUINS1_1. I wish that you would take some time and get farmiliar with SRB2's textures.
Whoosh, official levels. Essentially you're taking one of SSN's levels and claiming it as your own. Eww......
And boss fights. Boss fights. I'm sorry, 4 or 5 consecutive boss fights get just old. Not to mention the homing-ness of SA mode makes it too easy. Which reminds me, SA mode fails greatly. I game-overed due to the spike balls on the edge of the platform on the fourth one, in addition to the the spike balls around the boss itself.
The second real level. May I remind you that this is SRB2, and not Sonic Heroes. Flat stretches and flying over long stretches of void don't make a level work in SRB2. You can look at some other levels that work such as acid missle and the defaults, but this isn't the way to do it.
I applaud the effort, but may I remind you that a mod is made for the levels; levels aren't made for a mod. :/