Some folks didn't like some of the graphics, particularly for the standard aliens which were said to look like plastic! I didn't know so many people knew what a real alien looks like, you all must have been abducted. All standard aliens removed but to make up for this there are other changes.
Asteroids have a different appearance and take new paths, (spirals etc.).
After the initial level, you get 3x "Mo Time" upgrades (when you move, time moves) and you now get all the target designator upgrades.
As there are less of them, alien shots pack a bigger punch and move a little quicker to balance things out. Remember, the UFO does not get picked up by the target designator so keep your eyes peeled!
Enjoy.