Another good game I played in my childhood.
In Klax you have to catch falling tiles which you then drop into a field in order to build horizontal, vertical or diagonal rows of at least three same tiles to clear them out, much like in Dr.Mario or in Tetris. You have to accomplish certain missions (like acquiring a certain number of points or getting a certain number of horizontal rows). There are 100 missions (also known as waves), and you can warp 45 waves ahead by forming a big X on wave 6 or 11.
There are certain features in this game that I wasn't aware of when I played this game back then which I just recently discovered. For example, you can push tiles upwards to have them falling from the top of the screen again. And you can create tiles on your platform by simply pressing the select button. However, since this defeats the purpose of the game and makes it a lot easier to play through, I think it is a leftover on the programmers' part. I abuse these features a lot in my TAS:
http://www.youtube.com/watch?v=h1FsTgCdG5k
I used the Gameboy version as it was the version I'm most familiar with and I didn't like other ports I tried. This TAS can be improved upon a bit, but I don't plan to for now.