I'm not particularly into physics-based/puzzle games but still managed to yoink 44 coins! :D
I particularly liked your level design - new elements were introduced one by one, allowing me to get familiar with different mechanics one by one. Adding checkpoints was also a very good idea, although I think that sometimes the velocity vector is not zeroed after respawn (i.e. respawned ball moves in some direction from the get go).
One thing I had trouble with was controls - I often forgot where is "up" and where is "left". But it will always be an issue with isometric view and WSAD controls...
Overall a very solid prototype/base for a game!