Obviously great work getting more than 2 players working, its a good technical feat. It's a shame that you didn't get to sounds, and missed a mark on graphics for the center line.
The player join is a little unintuitive, and requires the players to navigate multiple menu screens -- I realise this is necessary though with multiple keyboard players, as with multiple controllers players could just ready-up with a button press.
One side effect of the player-join is that in two player mode I ended up with the left-side player using up/down (right-side of keyboard), and the right-side player using W/S (left-side of keyboard), which is backwards and a touch confusing.
These issues aside (and a few that I have highlighted in the individual CRA rows), its still excellent work, well done.