To me the world map looks mostly fine, except for maybe the hills on the up right floating in the air. I personally would use fewer waypoints on the path, but that's just a minor detail, I don't think the map is clustered with sceneries. You could move some of them a little though, so that they don't line up too much which makes things look more artificial than natural. Overall it looks good to me.
I played your episode. And I think it is better than most of the Boss Rushes that have been posted lately. First of all the levels mostly look appealing and bosses don't feel too repetitive, with a few exceptions. (The SMB2 Dragon Boss is the generic "Wait on the left until he stopped spitting fire, throw bomb at him, go to the left again, repeat" thing). But there are a few game design flaws:
-In a few levels you are in danger right at the beginning and barely have time to react. Already in the first level axes come flying at you immediatly. In the underwater level you sink down and die if you don't go up fast enough.
-You use odd speeds for some projectiles. The seconds Boss shoots insanely fast rockets. I spend my whole time looking at the enemy graphic to focusing on whether he is about to shoot or not, which wasn't fun to me.
-Many Bosses in the beginning of the episode are very hard (Just like Boss 2 because of the fast projectiles), while the later Bosses are easier.
-Possible exploits: Like grabing the throwable block from the second Boss and just stand infront of the boss for multiple hits, this wouldn't be possible with bombs
-A few 1-ups in the beginning would be nice, so that I don't have to navigate through the menue after every gameover
In the end I had fun playing your episode. I could see that you put more effort in the boss fights than the average Boss Rush creator.