"It's hard" is one of the most common parts to feedback I've recieved on mine ^^;
Which, is fair. I didn't want to give the player too much lull time, but went to far the other way. So now I have an aggressive spawn code that throws enemies at you about as fast as you can defeat them. Which was partially by design, but It still needs to slack off some.
I also botched the spawn code a tad so the toughest enemy spawns more than it should; far too common for 2-3 of them to spawn, turning the screen into a maze of bullets (whoops!
In some respects there might be a certain element of "get good" to it; for me the tuning felt "just right", so experience/knowledge probably goes some way..
....albeit given a friend of mine has played it to the point of breaking 6k points (I've barely gotten 1.5k!), the people playing it here are probably a better benchmark to go by~
Still, as stated it's hard to really get time for thorough testing/balancing, but as creators we probably should err on the side of "easy" compared to what we think's fine ^^;
Even if there's the odd crazy person who can thrash us at our own game