A suggestion, slightly change the colour of either the red ninjas or the red branches so the ninjas don't "disappear" when they fly in front of the branches.
And can you make the branches more like the branches in the original game and not just horizontal lines?
You really need the boss battles (bonus rounds) screen too I think,
this is a decent effort/port so far but it does need a bit of variety (like the other screen) to maintain a player's interest and not just become repetitive.
One simple trick that has worked in other games, even if it wasn't in the original arcade game,
is slight colour changes in the background as you get to higher levels, it gives the player a sense of accomplishment.
For example, remember in Space Armada, they just changed the colour of the border every couple of levels,
but you would say, "I made it to the second green screen level".
You could change maybe the colour of the sky as you go on, that would also give a sense of the day progressing for example, like they did in Frog Bog.
It's admittedly a small change but it makes it less repetitive.
Just my opinion, feel free to ignore it, I realize the game is still in its early stages but these are just suggestions from a player point-of view,
that you may want to consider.