Crazy emo, melodramatic narrator! Can't even look at a bird without getting some overwrought, unnecessary message about how Graham is sad!
For its flaws, King's Quest 5 really is a great game and one of the best of the series. I'm also in the camp that likes 6 better, but 5 is fantastic too. In fact some of the different areas of 5 are among my favorite locations in King's Quest. The desert, for example I loved. I also enjoyed the look of the Harpy's island and wish you could explore more of it. And Mordak's castle was very well rendered and designed. The music too is the best in King's Quest. As much as I enjoy the music from 6 and 4, there's just no comparison to the Willow's Song, Mordak's Theme and it's variations, and the original Cassima theme which later inspired Girl in the Tower.
And really, the flaws aren't terrible. The illogical puzzles didn't bother me much (except getting the emeralds out of the pouch and thinking to throw them to hidden elves.) And most of the flaws are more a result of the technology being new. Yes, the red X looks bad now, but the interface was new and it was no more jarring than the game responding to your command with, "You can't do that" or "I don't understand what a -blank- is."
I will agree with Katie that the mood could have been a touch more urgent in Serenia. Or rather, some of the dialogue could have been tweaked to be more realistic. I remember thinking that Graham and the people of Serenia were just way, way too polite. It seemed like every transaction you had was obligated to end with a, "Thank you, my good man, this will certainly prove useful in my quest." "And good day to you, sir. Stop in again any time." "I will, thank you." "Thank you!" "No, thank you!" Or something of the like. Maybe it was just me, but it kind of bugged me a little. At the very least the dialogue could have added Graham occasionally asking people if they'd heard of Mordak. But these are just minor criticisms. They're nothing that hurt the game in the long run.
The only thing that really bothers me about KQ5 are the voices. The game is much better without them. There's really not a single standout in the bunch. At best, the voices are passable, like Mordak and Icebella and Cedric (roll your eyes all you want, but you know that's exactly how an owl wearing a waistcoat and monocle should sound!). At worst they're a lisping narrator, shopkeepers reading their lines, and a guy making a really annoying growly wolf noise. I know that none of these guys are actually actors, that they were all designers, and yes the technology was new, but it just didn't sound good.
That's really the only major complaint I have with the game though. Everything else about KQ5 is pretty fantastic.