Mazogs A game that was as much of a marathon actually loading as it was to play. 15 minutes of your life would be wasted waiting for this to start; a lot longer if rampack wobble occurred.
The game involved trying to reach the end point of each maze in as few steps as possible whilst avoiding the spidery Mazogs. If you picked up a sword you could attack a Mazog blocking your path but your sword would only last the one fight so another had to be sought.
The only problem with this game was its 2D perspective, unlike the game below.

Arguably the original first-person survival horror game that spawned any 3D game since, eg. Doom, Half-Life, Wolfenstein, etc.
Running around a large maze sounds easy but with a T-Rex after you its pant-wettingly scary. Messages at the bottom of the screen would warn of impending doom: "Footsteps Approaching", "He's Behind You", "Have You Shit?"
The fastest game ever - you barely lasted a minute before being eaten by the Zippyesque dinosaur.
Monster Maze

49er Just 20 short of a sex position.
This broke the mould of ZX81 graphics by introducing hi-res. The miner looked like a stick freak and the rats looked like, er, well, rats.
A bit like an early boulderdash clone featuring the usual underground fun like knocking out the wooden supports and dropping boulders down shafts.
Perhaps this would have been better if dropped down a shaft too.

Another of the ZX81s best.
Run around the maze avoiding being eaten by the snake. However, by running across the tip of its tale you shorten the length of the worm until it is head only.
Bonus feature: this game came with a maze construction kit enabling you to create your own levels.
Top marks for everything but sound.

Night Gunner Re-enacting Focker dogfights over Nazi Germany in this World War II simulator was great joy until you realised the depth of the game.
Enemy planes made out of "O"s and minus signs, with a full stop for a pilot, would sweep randomly about the screen. You could attempt to maneuver your crosshair and shoot the b*st*rds out of the dark sky.
When your ammo was depleted it was game over.
If Hitler had trained his forces to fly using this game he might have made a bigger impact in the Battle of Britain.

One of the later releases towards the ZX81's demise and Speccy's take-over bid.
Spin the turret around to blast the flying saucer scum outta the city. Careful you don't ionise the buildings though.
If Osama Bin Laden got his hands on one of these he could have taken the whole of New York in one afternoon.
You wouldn't believe how good the ZX81 could cope with multi-layered parallax scrolling.
City Patrol

Sabotage Not the superb Beastie Boys track with the Starsky and Hutch-alike video by Spike Jonze but an equally good blaster involving stealthy bomb laying or saboteur hunting with a gun in an explosives factory.
Choose to be saboteur or warehouse patrolman. If saboteur, just plant bombs and blow shit up, including the guard. If guard, try to shoot the saboteur before he blows you up.
Simple gameplay with addictive qualities that may have you re-enacting in real-life.

The ZX81's attempt at recreating a coin-op classic.
And it succeeds with triumph and graphics made from letters.
All the barrel-jumping fun of the original as you scale the grey fuzzy girders to reach the lovely princess "Inverted J".
Watch out for Kong's bikini tan - he really should have gone topless instead of covering up on the beach.
Crazy Kong

Namtir Raiders A fantastic shoot-em-up like no-other seen before (on the ZX81).
3 waves of different attacking aliens then a wild mothership to defeat. Just when you thought you'd beat them, there were more but even faster.
This game had 99 levels of speed. The wise started on level 1 and the crazy suicidal started on level 99.
Which are you?

The best Space Invaders clone on just about any machine.
Packed with other classic games including Snake Byte (above), Michael Orwin produced one of the best compilations ever.
Invaders involved the standard storyline of boy meets alien, alien meets boy, alien and boy fall-out over same woman, alien shits on boy, boy blasts alien scum from the skies.
Like Namtir Raiders you get to chose how quickly you want the Invaders to die - slow and painful or quick and satisfactory.