It was a cool surprise to see this game was an expansion to Rebound 2: Electric Boogaloo, and I'm satisfied by the way you added to it, though I have an opinion I would like to express
Visual-wise, the new areas and the ones that changed over the time between both games kept their appeal and quality; I'd say even improved the immersion; the textures and new effects were really well performed, my favorites are the snow and the new power up ones
Gameplay-wise, the game keeps it's easy-to-learn hard-to-master concept, and gives more new fun ways to experiment with them; I really like how the new power ups added more exploration options, and I wish these new mechanics were given more use
About the map expansion, here's a personal opinion I would like to voice, ands is about the world-map shape; I think the exploration element on games are greatly improved when you present an square world map filled with rooms; like you did on the first game, think about the NES The Legend of Zelda's world map, when you are new to the game, and find there's a room at the right, and a room upwards; you'd expect there's a way to reach a room presumably at the nor-west, and feel a sense of completion when you get to it
The expansion rooms are mostly skewed to the left, some has a couple of rooms below, some a couple of rooms upwards; but is more about going left than trying to discover new map parts
A way I think it could be achieved is to put more explosives like you did in the prequel, giving a reason to explore previous areas backtracking while filling map gaps
Other than that, the game keeps being a lot of fun to play, and offers great satisfaction all the way
Music and sound effect-wise, they fit perfectly the mood of the areas and game, and each are recognizable and sticks on you; that's about everything game music should look for, isn't it?
Overall is a great game, which is leaves me with will to replay it no matter how much times I've done so; I attempted to get everything on my first play-through, but found the goal before going the other places I wanted to lol; here's my stats!
96% map completion
After that, I tried to make a perfect play-through of the game, with all coins, all map percentage and without re-spawning, my personal best time is 7:17 so far!
It was hard to fit the video in less than 8MB, so I had to make a consensus with the resolution and audio's bit-rate, my bad lol
I can already say I'm a fan of your Rebound series!, I feel I'll always have fun replaying the entries you have made so far on it, but can't help but hype for a new one too! That would be amazing! Props DevEd for creating such an enjoyable series!