I'll have to try it before I can judge, it's somewhere deeply buried in my backlog. Of course, visual novels aren't always just reading, you also make decisions, for example, but as soon as you can move around freely and examine objects, I think I'd be hesitant to call it a visual novel.

I work pretty hard to not use a walkthrough because it always makes me feel a little dirty if I do. I only used a walkthrough once though out the three Deponia games, so I feel like their difficulty was about right. I hate it when adventure games are too easy, there should be a bit of hair pulling.
I'm inclined to agree. Phoenix Wright games become more than visual novels because of the non-linear investigation sections.

Well, that's the curse of adventure games. I don't have much time to play games, so when I do find the time, I certainly don't get any pleasure spending three straight hours trying to find that one hot-spot that will allow me to advance. But using walkthroughs too much just kills the game for me; what's the point?

Some adventure games give you the option to highlight all objects you can interact with; I like that a lot, because if I get stuck, I'm stuck on an actual puzzle, not "You fool, didn't you realize that you could interact with that nondescript patch of grass?" I'm much less likely to use walkthroughs for those games.

It depends on the game. If the game itself and time in the game (ambiance, lore, characters, etc) are entertaining, then I will consult a walk-through as much as needed.

However, I still expect logic to be involved in the puzzles. Most games have at least one puzzle that not everyone will get. Its impossible to make the game challenging for some without alienating others. But I do get frustrated at puzzles, where after trying for hours, and then consulting a walkthrough... it still doesn't make sense. I may be able to advance, but the devs get some bad karma from me :p

I was watching a movie that seemed to copy itself from the Scream franchise. It was a horror who-done-it. At first, I thought they did a good job of keeping the audience guessing, and at the very end, when they revealed the killer, it was someone never mentioned or introduced to the audience before. While the writer/director likely patted himself on the back for being clever... no one enjoyed that movie and few will likely watch his next. Games are similar. Each "gotcha" that couldn't be logically deduced is a weight on the scale towards alienating your fan base. We WILL go back and look for the clues and if we can't find any warnings, hints, or pointers to the logic used... that is bad.

So while I will use walkthroughs to finish a game (especially the good ones), frequent requirements of them will weigh heavily on weather I play the sequel or not. (or other games from the same publisher).

I do sympathize with devs. They get it from both ends. "the game is too hard!"... "the game is too easy!". So I cut them a lot of slack if I can eventually find out how someone used logic to solve the puzzle.

While I prefer not to use walkthroughs in adventure games, my willingness to do so depends to a large extent on why I am stuck. If it is obvious to me what the solution to a puzzle is, but I just can't figure out how to make the game accept it, then I don't have many qualms about using a walkthrough if I've been trying long enough to get frustrated. Examples include situations where I obviously need a certain item or hotspot that I missed in one of the previous six rooms, and the solution is just to go through and pixel-hunt them all again. I'm willing to do one or two re-sweeps for missed hotspots, but if that doesn't find it I generally at least look up what room I'm supposed to be in - it's not like I'm giving up on any sort of intellectual challenge, it's just busy-work, so I don't think there's anything shameful in cutting it short.

On the other hand, if the game has thrown me a real puzzle worthy of my respect (i.e. one that involves more than just "rub object x on hotspot y"), and it's clear that I just haven't done enough thinking about it, then I am far more willing to sit there for days trying to figure it out.

I've discussed it here before, so to me the thing that makes a game a game is that there is something trying to impede your progress (be it puzzles, action sequences requiring good reflexes and eye-hand coordination, tactical thinking, or whatever; that's mostly how games are categorized into different genres, ie. what is that impediment).

Otherwise they are just interactive... something. I know many disagree with me, and I admit something like Minecraft in creative mode is some kind of borderline case. In any case, even if I had a virtual tour program where the world interacts with me, but there is nothing impeding my progress, then I just consider it as a interactive virtual world tool, not a game.

Like. MS Paint is an utility and not a game, even if it can be quite fulfilling to create pictures with it. Minecraft in creative mode is a glorified version of that, a tool to create something virtual. Or a 3D CAD program that lets you create a virtual home and move furniture around there, is it a game?

Note though: the impediment can be quite light though. For instance, an adventure game without puzzles, there could still be an impediment that you need to find different places and objects before you can progress, even if there weren't actual puzzles impeding you. A bit like the hunt the objects adventure(?) games.

It's simple.
You are playing a game for fun.
If you have been stuck on a puzzle fo the point of frustration where you are no longer enjoying the game then you use a walkthrough.
And some people just do no like wandering around endlessly trying to find what to do or where to go next.