The game's engine has been updated: the ancient Cocos2d-x is out, the new Axmol Engine is in. Steam integration and game controller support have also been upgraded to their latest versions.
And what does this mean to players?
The game now requires a 64-bit computer, as is the case with any Windows PC released in the last 10 or more years;
It runs noticeably smoother and input is faster - gone is the lag that could be felt sometimes.
Old save files aren't compatible with this version, but this is the format that the game will use from now on - meaning that players will be able to import their progress into the full game;
And... that's it. It may not seem much, but the game clearly looks and feels better now, specially on older computers.