I've first played upgrading only power and lasted quite a long while, the ghost-like enemies didn't directly go after the guy in the middle, it just got tougher to defend when the screen filled with enemies. Some of the times where i lost in example with one of those ghost-like enemies getting close to the middle guy i thought i was fine, but they kind of triggered the game over even if they were a bit far.
It's a fun game and well polished, the issue where people is not getting SFX is because the value defaults to 0, so when you load the game for the first time, slider's values are at the minimum, in case that helps locating/fixing the issue. It seems to be the first time ever that you load the game only. I've refreshed to reload it and I had the "sound" maxed to test before refreshing, and loaded as 48/48 (both sliders at 48).
Lastly, the tutorial. I know it's on the website, but try to always have it inside the game as well, even it it's simple/common controls.
Cheers ;)