I reached level 7 of 10 and got a score of 5452!
I took an embarrassingly long time to figure out how to use the bombs! xD
I'm not sure what "L Strg" is on the key board?
Sound effects were great! Reminded me of the old arcade like DOS games I had when I was a kid. The graphics are fine the way they are at the moment as well, keeps well with the theme.
The way the aliens move around seemed a bit random to me, I felt like a lot of the time I just had to wait for them to come down.
I like how they build up there base, its almost a reverse tower defense! :P
Maybe what this game needs is a few more abilities and power ups.
A lot of the time in the later levels i felt like i spent all the time moving and could not get up to shoot back.
If there was a temporary shield power up that you could time to go on the offensive that would of fixed that.
Also things like a rapid fire powerup, deflect bullets powerup and slow enemy bullets powerup would be cool.
You could make them like Mario kart weapons, you can hold one at a time and "fire" it when you think is best. That way a player can't hoard them in the early levels.
Overall, a fun little game with potential! :)