Ok I gave this a playthrough and well, it's fun to play! I especially liked how unconventional your underwater level felt. If I had to guess it'd be because of the spritework: how you arranged groups of enemies, etc. Very nice work with that one. Only thing I'd suggest design-wise is to make it a bit less cramped at parts so the player has more space to move around. The grass level was nice too, although I feel like using lotuses in conjunction with those other sprites can be a bit overwhelming for a first level. Also you should probably capitalize the "M" in "Such mountains" so it matches with the other level names.
My biggest gripe with these levels is the music choices. I don't think DKC2 Gangplank Galleon fits a pure grassland level, nor does that one theme in the grass + layer 3 water sublevel in Epic Lake fit it well either.
I also don't like the color you picked for the shadow of the grass in the first level. It has too much orange in it. Try going with something "colder", like this
. The underwater level also has some bad palette choices, like the brightest FG color being too saturated and the BG being too bright and using the same hue as the FG, which makes it blend with the latter. Try something like this
instead. I can give you the .pal for both levels if you want.