Lookin cool Mat!

The composite is nice and clean (aint alpha grand ). In a couple of shots the UFO looks a little dark. This is tricky to solve without rending a dozen passes with reflections/shadows/hilights/etc. A quick fix may be to add an adjustment layer in AE and use that to remove some hue or even make it sepia (there are even a few AE plugins that can give ya vid a nice movie look).

Also, if you want quick special effects, grab the trial of Particle Illusion (from wondertouch.com) its great for lasers, explosions, dust, smoke, etc.

I disagree with Neo on the pace of the shots. I dont mind the quick cuts. A bit of fast paced action movie music in background would certainly sell this shot for me. But I do have 1 suggestion - at the end where the gun pops out and fires, we then see the victim look scared, points up then gets hit and falls back. I think a re-cut might add some pace. Try to have the gun draw - victim react and point up - cut back to gun which then fires - then back to guy falling back.

Remember to have loads for fun