The biggest thing seems like you need to “master” the sounds better so that they are more similar, particularly in the spatial image.

• It seems like some of your sound effects are stereo, with very wide spatial image (e.g jump sound). Others are very narrow/mono. I'd suggest converting all sounds to mono so that they are consistently spatial, then using the game engine's panning capabilities to create stereo image by panning according to the location of the sound on the screen.
• The sounds are very “dry”, e.g. there is not much ambience or reverb. Try adding either background ambience (e.g. wind noise), and/or use the game engine to add reverb to the sounds. This will also help give the one-shot effects a more coherent spatial image.
• Consider the relative levels of the sounds. The jump sound seems too loud to me, while there is no sound for when landing. Seems like it should be the opposite. There should be a significant dynamic range between the loudest and quietest sounds, so that not everything is mixed at the same level.