Nadir's screenshot post about Sivion made me remember that I hadn't actually completed it despite starting a few times. Generally remembering it in a good light, I took a crack at it again this evening.
Sivion has a few neat short parts, but one the whole, it's a bad game.
I started off pretty quickly, although it occurred to me that I just remembered all of the beginning trades and talking sequences from the times I first tried the game in 2004. What begins as an interesting quest to stock up on arrows and gems eventually becomes deadlock without cheating. It is so fucking easy to miss some necessary items and areas and yet keep bumbling on until their absence makes the game unwinnable. In one or two parts, buggy objects prohibit you from finishing without zapping. Many boss objects talk to you in blue message boxes while you're shooting them, which sucks because pressing shift and arrows in a message box closes it immediately. The game, which is superlocked, states in the editor that it has been beta tested and has no errors. >:(
Besides the obvious stuff, like having to input a password (which requires knowledge of some other game) to start playing, and the dark+invisible mazes, trading puzzles are often very obscure. There is no indication that some random conversation option is the only way to get a key, and that afterwards you'll never be able to get it again. Most conversations are displayed as flashy marquee text at the bottom of the screen, and two conversations have a tendency to overlap, making both unreadable. (Best example of this being the prison.) Every forest area is a ping-pong path maze begging to be zapped through. Most bosses, when shot, wait for one idle before zapping labels, meaning you can hammer a boss with most of your bullets and only deal one hit.
The game feels like it's split into two bits: the first area which is generally crappier but more interesting, and the second area which has somewhat tighter programming but less going on.
I do like some bits in Sivion, like the glinting, shiny gold in the mines, and the torture room. I also like how if you revisit the forum a new band will be playing. And the djinn store, that part is great. But god damn if it isn't one of the most tedious ZZT games I have ever played.