Pretty faithful, though with a few bugs
Couple of things I noticed. Firstly you missed an important part of the space invaders game - the speed. The invader speed should depend on how many are left on screen; when there is only one invader it should be moving very fast. The second one was a small bug - when you shoot a UFO it stops the music. They should (I think) be pretty easy to fix.
Other than that it was a nice and fairly accurate space invaders flash remake (even if most of the things on screen were constantly changing width or spinning). You get points for not making a horrible 'Sonic has to shoot the badniks before they invade green hill zone' (or whatever you happen to be into) version.