Contrary to the label on the tape, these games all loaded and ran in an unexpanded ZX81 - you don't need the 16K RAM. All examples of good, fast, machine code programming: they are loaded first time and the instructions are comprehensive.
In Overtaker, you are driving a car. You have to increase speed and weave in and out of the traffic - and the faster you go, the more you score - unless you crash! An addictive game.
Missile Man is the best implementation I have seen of Invaders on a 1K machine. Four rows of aliens plus one swooping bombard your battery, and the explosions when you hit an alien are impressive. The game plays well and is great fun.
I am surprised that Starfighter Pilot fits into 1K. You can flip in and out of hyperspace, with stars rushing towards you, and in normal space a landscape scrolls towards you with missiles rising from its surface. You destroy them by positioning your gunsight over them, whereupon they explode. It's difficult to get a good score, but fun trying.
Guess what Greedy Gobbler resembles? You have four ghosts chasing you as you eat the food capsules, and the power pills turn the ghosts grey long enough for you to catch them. A clever implementation.
Don't be misled - the last game, Extra Terrestrial, bears no resemblance to the film. You are in an alien spacecraft orbiting the world which you attempt to exterminate. It's only a matter of time.