Since this came up in the “Do you use a guide?” thread, I was curious what games people found hardest to get real endings in (or happy endings if you always end up with a real ending) without using a guide. Of the games I have played so far, I think the hardest ones would probably be Kana and Tsukihime.
Snow Drop was fairly difficult. The game’s system was fairly confusing, and even once you knew what was going on, it possessed exacting requirements to get into the “real” portion of the game. It’s a fairly realistic mechanic in that important events happen at a particular place, at a given time, whether you’re present or not. Some old all-text adventure games used this system. But I feel that in Snow Drop’s case, it was poorly explained and, while clever, it didn’t actually improve the game.
MinDeaD BlooD. Gun-Katana.
Either EXTRAVAGANZA or MinDead Blood, but I think EXTRAVAGANZA is a little bit harder. Gun Katana is also rather nasty, but I think it’s slightly easier than the previous two. EXTRAVAGANZA uses a ‘chart search’ system to determine your choices, and you can see prior to making a decision, what scene will result from your choices, which makes the system sound easy enough. 
But the sheer number of decision points combined with the branching paths plus the need for your choices to be pretty much perfect to avoid a bad ending makes this game pure hell without a walkthrough.
This image is from the opening chapter of EXTRAVANGANZA (I’ve cropped out part of it to avoid potential spoilers). Each of the small light blue rectangles on the bottom left of the screen is an individual scene (77 in this chapter, and some of the latter chapters have just as many). The stars above a scene refer to the number of variations of it, and which version you see depends on the choices you make prior to it. Although some of the scenes just lead straight onto the next one, slightly over half of them have a choice attached. In some cases, the choices are also important for a future chapter, and may affect the paths or choices that are available there.
It’s an innovative way of presenting the story, and it makes you appreciate how much thought and planning has gone into it, but the difficulty level is completely unreasonable. (and even with a walkthrough, there’s a significant amount of backtracking involved to see every scene in a chapter).
Edit: I should add that with MinDead Blood and Gun Katana, the ‘default’ endings in each game aren’t necessarily bad and can be reached fairly easily (the challenge is more in figuring out how to get on the major routes), whereas in EXTRAVAGANZA, without using a kouryaku you will die. A lot. That’s not to say that there aren’t other outcomes, but they are all difficult to reach, and are quite a long way into the game.
I’m limited to translated games, unfortunately, but of those I would say Casual Romance Club, Kana, and Doushin. (Did anyone other than me play that one? It never gets mentioned.)
Ignosco already mentioned the obvious ones, but I’ll throw these out there:
3days - Lots of choices, lots of bad endings, very unintuitive.
Flutter of Birds - Unintuitive choices (most choices involving you having to make a location guess), relatively small choices choosing which ending you get (which are again unintuitive), RANDOM EVENTS #@#*^#@ (if stuff doesn’t happen exactly right, you can make your route unwinnable, and how are you even supposed to KNOW that shit without a walkthrough), you can only save once per day (rather than anywhere, as we’re used to nowadays). This game came out in 2001, which is simply unbelievable, because the engine is a travesty - the sort of thing you’d expect in 1996. Great game and only really takes a walkthrough to counter most of that, though.
Kusari - damn hard. Quite a lot of choices, many of them important (and can take a long time to punish you if you get them wrong), but the ones you have to make are usually logical at least in retrospect. You also have a running inventory and map (showing your current location) so that making intelligent choices is easier. It’s still a damn hard game, though.
Would you believe I completed most of its routes without a kouryaku? Of course, in my three first games, I got Miama, Ibuki then Tsubasa dying on me, but… ^^;;;;;; Anyway, I personally didn’t find it hard. All the contrary, all the randomness made it fun to play!
I only used a kouryaku for Megumi because I had absolutely no interest in her.
May Club and Doushin Same Heart come to mind rapidly.
Talking only about eroges, I found crescendo to be a bit confusing, so had to use a guide. Ai Yori Aoshi too, but I cudnt find a guide 
So the game is still incomplete. Snow Sakura is simple but I needed a guide at times.Slave Pagent: didnt need a guide at all. Thats all the games I have played so far. 
I’ll believe it; after all, I finished ONE, MOON. and MinDead Blood without kouryaku >_> oh god
Could you explain the latter? It’s been a while but IIRC Ciel is very helpful about informing you how you went wrong. So I don’t see how it could be hard at all - the point checks are generous and only unintuitive choices punish you pretty much instantly, making it quite easy to reload to your last save.
Worst one for me so far is definitely MinDead Blood. The whole choose where you want to spend the day idea is interesting but there’s little to no guidance on where you MIGHT want to go. That and Yuka has a tendency to be less than gentle with you if you screw up.
Save for Shun, I didn’t need a kouryaku for ONE either: it was pretty straightforward to me, with just text choices to make. I personally think something like good old *kyuusei games (or the recent “MapleColors” series) far more difficult, with a timed free move system. ~_~
…then, you have “Touka Gettan”. :mrgreen:
While it was easy to get an ending in Sagara Family, getting to the solo endings was really difficult, as you had to be on a certain path, then had to answer Ruruka’s question set correctly to get on the girls solo paths. One screw up (which path you were on, then if the Q&A session didn’t give the right girl’s description) and you got one of the 2 pair endings.
ymk can be hard without a guide it is easy to get the bad ends
Touka Gettan doesn’t fit in this category at all, because it’s not just hard.
It’s not PLAYABLE.
You can’t finish it without a kouryaku, and you can’t finish it WITH a kouryaku. YOU JUST CAN’T FINISH IT. EVER
At least, that’s the excuse I’m using. I think it’s going to be one of those ‘eternal backlog’ games, because I’ve never had the impulse to go back to it. Not even once. A game with Carnelian art can bring me to pull off superhuman feats in order to complete it, but that’s just not enough with Touka Gettan.
Ah yes… I forgot about EXTRAVAGANZA… I agree: total pain in the ass to figure out.
Gun-Katana turned out to be a nightmare for me, because of the Merit Awards (basically like Achievement Points in an XBOX game). As per the usual for Cyc titles, absolutely no effort is given to reveal what the conditions are. However you can’t unlock the Secret Mode (with all the developer and voice actress interviews), without unlocking all the Merit Awards first. On top of that, some of the Merit Award conditions are plain insane and require cheating with the “secret uber gear” hidden in the game. Which surprise-surprise, are also nearly impossible to find and locate.
While I played the game entirely with a guide (since I had limited time to borrow it from my friend), when Ciel talks after a route, she didn’t seem that helpful to me.
I think tokimeki Check in was pretty brutal. The choices were so vague that it sucked. To make matters worse, the skip feature skipped unread text so you couldn’t redo things as fast because you’d miss dialogue.
IN my colection, the game that still takes the cake for being unplayable without kouryaku - and being too good for being spoiled by using one is Touchy’s “???” - I started playing it years ago - and still refuse to use a kouryaku for finding the real ending.
Oh, and apparently WAFFLE’s “???” is quite a handful too (at least getting the sister’s route!) - and as far as I know there still doesn’t exist a kouryaku for this one! :shock:
clannad, kyou’s route (for the good end) was impossible without a walkthrough.