One recommend: reduce the player's X-hitbox by 1 px on each side. Seems like a lot of movement is (+1, repeat +2) and it makes lining up with tile spacing impossible; and a lot of the harder layouts require pixel-precise positioning for navigation.
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I remember playing this a lot in 2007-8; a rightly cool concept well ahead of it's time. It became hard to find, so seeing it made available here is greatly appreciated!
I do hope life gives you some time to revisit the concept at some point - I'm also being swallowed alive in a non-gamedev career right now, and it kind of sucks trying to find time to do stuff like this. Rock on, and good luck in your endeavors!