I used to have this one in a G.B. Max tape, the infamous italian pirate, with the title Krion and it was such a well done hack that not only, as usual, there were poor instructions accompanying the game, but the game itself crashed after five seconds into playing. Finally, now I can play it at ease, with proper instructions, and without fearing a crash, if not by my costantly crashing PC, of course.
This vertical shoot and dodge work comes from the mind who authored Nonterraqueous and Soul Of A Robot forMastertronic, appreciable sci fi maze efforts, but for this sequel of the previous two [or anyway, the WoS archive lists it as a third episode] Stephen N. Curtis lent his programming skills to the then newly born Codemasters. Is it really brilliant as it should? Well, for an economical[*] effort it's not bad at all, and, in fact, I think it's pretty good, actually, notwithstanding the simplicity of the gameplay, the total lack of depth or special features or variety - but not all games can be complex and fancy as Space Invaders, after all.
[*] by the way, so economical that they could afford only two enemies on screen simultaneously.
What's the trick? The trick is that once you learn how to play it, it can become quite fun and addictive, at least if you manage to not get blind because of the monochrome of the game, a game that asks you to be very attentive to the background appearance and conformation. In fact, you must learn to distinguish various square elements that can be just fatal barriers, or time shift things - which will annoyingly bring you back to the start - or more useful features like extra-lives [L], fuel [f], shields [arrow], acceleration [plus symbol], deceleration [minus]. There are different kinds of monochrome depending on your speed mode, which is determined by the squares mentioned above, while the border becomes red when the shields are - briefly - activated, which will allow you to fly through the droids, or spacecrafts, or whatever they are, without exploding. There aren't tunes or jingles, but I find the explosion sound effect quite satisfying. If you'd like some minutes of mindless destruction and fast-but-not-too-much action, Terra Cognita can be quite entertaining.