Castle Dungeon
In the interest of full disclosure, this was one of the first ZZT worlds I played that had STK in it(and that I finished on the first try). It may be the only game that refers to slime as ice-cream!
Board number notwithstanding, this is a short adventure/action game which involves you having to escape the Booplop dungeons, reinfiltrate them and get out again. The gameplay is fairly varied with some invisible wall mazes, action boards with a mix of built-in enemies and original ones, one transporter maze and two slider puzzles that are easier than they look. The game is very generous with health and ammo, to the point that you can just deal with all the built-in enemies in the game by letting them hit you. There aren't any obvious bugs in the game, though it's possible to get an inevitable game over late in the game if you don't poke around in the opening dungeon enough.
A lot of the game being in gray and dark gray, presumably to reflect the 'dungeon' setting which works rather well. The title screen has a rather neat abstraction of a castle. Otherwise there isn't much to write home about graphically, except for some nice chandeliers at one point. Theere are a few bits of music which fortunately aren't repeated ad nauseam.
Overall this is an average old-school ZZT game with some STK window dressing. With the author fortunately deciding not to cram boards with 'things to do' on the whole, it never gets tedious. However, I wouldn't recommend its sequel 'Booplop' which feels more tedious without really improving on this game either gameplay-wise or graphically, has a lot of cheap deaths and suffers a lot from the Try-Me Trap.