The best thing about Glowgrass is the setting. It's an interesting premise, though sparsely implemented, that does a pretty good job of drawing you in.
The environment is pretty small, and the puzzles for the most part are quite simple - though as another reviewer mentioned, there are some flaws in the implementation. For example, if you throw x at y, you are told that you can't reach y with just your hands! (Spoiler - click to show)The really irritating part is that you ARE supposed to throw x at y... but if you specify the target, you're screwed.
The conversational mechanic is also a little unintuitive - if you're having trouble, just realize there's an ABOUT keyword, and it's crucial.
If you don't get caught on the rough edges in the mechanics, Glowgrass will probably only take you 15 or 30 minutes to finish, if that. It's worth playing.