I agree with all that was said by swoopie, and I think that it should not be by design that you eventually just can't keep up. For example one of the things that makes an endless survival game like CoD Zombies great is that you can go as far as you can, purely by development of skill. BUT if you mean what you say then you don't want it to technically be endless, so you could make there be a final wave with a boss or something. Or maybe even like after X number of minutes, there's a boss and defeating it within 1 minute makes you win.
However, my main feedback that came to mind after playing was that there should be one or two additional enemy types that occasionally show up with a different kind of attack. Or even stationary threats with significant health which buff other aliens nearby.
But I like it, overall. The music really made me vibe out to the nice speed of gameplay, and I found auto-shooting weird at first but after a minute I liked it.