Try to learn how to draw, program and come with original ideas before making something.
Good concept, but as previous players have said, I could move to the side of the map and shoot continuously for hours against flappy bird till the score goes to whatever max value you can go (which I assume is infinite as there is no health bar on flappyman).
Not great, nice colour, but there was no sound or classic ultra man sounds OR music. MASSIVE FAIL! If you are gonna do a ultra man vs flappy man flash, you gotta make the player believe he is playing an ultra man game!
Also, your title screen was waaaay to dark. You also needed something like 'press space to start' coz I thought i had to click on the screen initially.
Also, maybe giving the player an option as to who they would like to play would be quite nice.
Again, idea is great. However, it is poorly implemented!
Impossible to beat, nothing new, dull.
So here's the deal as to why you've got the grade you've got for this game: In the first two minutes of the game, I moved to the very left corner, and then began blasting and only have to jump over the three birds sent over from the very right and it then presents no challenge. Fix that up, bring it back, and it may slide by judgement, however, as it is, that one flaw, in a simple game, makes it a huge flaw.
This game is really bad, for one thing you didn't give us any warning, there's no music, no medals, and there is no effort at all. I can see why you said this is a very unpolished game because this game is exactly that unpolished, this game sucks and it is one of the worst games I have ever played on the site.