King's Quest IV is a great game. In fact, I'd go so far as to say it's probably as close to perfect as King's Quest has gotten. That said, it's not my favorite game. As an example, it's like when a band does a song that is literally just perfect. It encapsulates what the band is all about, the instrumentation is perfect, and it's just the right level of produced. Anything added or taken away would kill the perfection. That said, it might not be your favorite song. There might be another song that you like the lyrics to, or the music of, better. Put another way, it's like Lord of the Rings. On a purely technical level, I think you'd have a tough time arguing that Lord of the Rings wasn't the best movie ever made. It's scope, the fact that it successfully filmed an unfilmable novel, the sheer size of the cast and extras, it's just the best. That said, it's not everyone's favorite movie. I'd include myself in that. I love it, but it's not my favorite.
All that to say, I think that KQ4 is basically a perfect game. The puzzles are just hard enough without being impossible. The game changes enough in its fetch quests that it never becomes tedious or repetitive, and its roaming hazards actually serve a purpose. Technically, KQ2 did that with the dwarf and KQ3 did it with the bandits, but the ogre in KQ4 felt more central to the plot. Mainly because you had to go search him out, whereas the dwarf and the bandits were more a part of exploring the countryside.
The tone of KQ4 was also fantastic and very dark. Until MOE I'd say it was the darkest KQ. And really, it gives MOE a run for its money. And the fact that it accomplishes that with the older graphics and sound whereas MOE had a 3D environment you could immerse yourself in might make KQ4 the darkest out of all of them (adjusting for inflation, or whatever you want to call it). Tamir, despite having more residents than any other game, dead and undead, still feels incredibly empty. But not in a bad way (like Daventry in KQ1) but rather in a way that evoked a feeling of hopelessness and barely controlled despair. And the further east you went, the more the feeling of dread grew. Areas like the waterfall, which in past games would be a nice little place, actually felt foreboding because of the graveyard, the proximity to Lolotte, and the troll that was lurking just behind it. The land itself was a character in the story. KQ2 did this too to a lesser extent. The east side of Kolyma was enchanter territory and came to an abrupt stop with the mountains and the poisonous lake was always off-putting. KQ4, though, did it better.
I'm rambling and gushing, so I'll cut it off here, except to say that Rosella was a great heroine for the game. After Graham, then Alexander, then the implication that Graham wanted Alexander to carry on his legacy (he threw his hat in your direction) it really was a big step on Roberta Williams' part to make Rosella the star here. It clearly was meant to be Alexander if they weren't going to continue with Graham, but Rosella took the series in a new direction and brought the royal family into the story more. Yes, again, KQ3 did that with Alexander, but if they had just made Alexander the new Graham in the games, then KQ3 would have been seen more as his debut, not as a widening of the narrative to include the whole family. KQ4 was clearly saying, "This is about the whole family now." Plus, at the time, it was unheard of to have a female lead. Not only did KQ4 do that, but they elevated Rosella from being the simple damsel in distress, made her adventure wicked dark, and had her not get the guy in the end because she didn't want him (and because Edgar is creepy clingy.)
So those are my thoughts off the top of my head. I'll stop there since I don't want to post a wicked long dissertation. Oh, though I do want to add that the nude patch was just weird. Maybe pixilated nipples just aren't my thing. Oh, and the implication that Rosella isn't a natural blonde? Just unnecessary!