Not that bad!
When I first saw the blank background on the title screen, it didn't look like it would be that good. While not particularly good, it's at least playable. The best part was how you had so much mobility and were able to easily shoot the enemies down. I think there might be something wrong with the audio because it seems out of sync. For a demo, this actually wasn't that bad. Demos can be good if you really put time and effort into them.
I suggest you not make the main ship so small. There could have also been more detail in the background with perhaps some stars. I don't know why Patrick and Spongebob appear there, but they're still cool. Their sprites are actually really well done, just to bring that up. You could maybe also make a wider variety of villians.
THANK YOU! jeeze, i thought it was impossible to get a little positive reinforcement here in newgrounds. okay, the ship being small is a bit odd and it could use some background i guess. as for spongebob and patrick... can't quite explain that one.
Wouldn't be worth it even with gameplay.
All I see is another bog-standard amateur shooter with a single enemy type, spawning in random patterns instead of the synchronized formations that gave them any character in the game you're trying to rip off and with no interesting terrain to even begin breaking it up.
So sure, you can whine that this is only a demo and you'll add them later - but what little content you have here frankly isn't worth demoing, and you don't get credit for things you're imagining you're going to do later. Only for the things you actually accomplish. This shouldn't have been posted at all.