I haven't played many ren'ai (relationship/dating sim) games, though I've been expressing more interest in them recently. Actually, I have to say most of my experiences with them have been pretty bad.
When you meet a new person in life, you typically don't know how to react to them: what topics to bring up, which to avoid. You're in a feeling out mode, trying to get an idea of what the other person is like without stepping on a conversational landmine. One problem I have with ren'ai games is that I feel like this period never ends. I actually have to worry about two people: the character I'm ostensibly controlling AND his conversation partner. For example, it's not uncommon for the game to give you a choice between two answers which seem fine, but one of which will send both you and the conversation partner off the handle, while the other proceeds to an amiable conclusion. These choices may be indistinguishable, or they may be designed so that you have to say "the wrong thing" in order to get the right result. The worst part of this is that when the player has already realized they've hit a conversational landmine, they frequently aren't given a way out. Instead of analyzing how the other person reacted to what they said and perhaps apologizing, perhaps calling them on something that they're being unfair on, your character may instead just go off in a huff or have a hissy fit right then and there. You're never given a chance to adapt.
This rather leads into my second problem, which is
personality quirks psychoses. Your main character may be healthy or most certainly not, but I can almost guarantee you that the surrounding characters will be insane. Oh, that's not how they put it. They're depressed, or shy, or acting-in-your-best-interests-really, or possessed, or any number of other things, but it's usually taken to such a ridiculous level that apologizing for bumping into a girl you just met could result in you being skewered with a knife for your impoliteness. No matter how happy the character appears, frequently they have a dark past/horrible secret/inexplicably committed murder/something. This is how you get conflict in ren'ai games.
Ren'ai games are supposed to be games, but they don't feel much like them. Due to the above issues, you could find yourself heading down the wrong path because you did what seemed like a good idea at the time, and it turns out that decision was an unfixable error. Want to go after a particular character? Better make up your mind, because if you accidentally end up going down the wrong character route because you wanted to see what your friend was doing instead of chasing after your love interest, you're then faced with the fact that you probably didn't even make the right decisions earlier in the game and are now screwed into a bad ending. You're rarely given enough clues to figure out what you're supposed to be doing to get the route you want, so it's more like Russian Roulette than anything.
Part of the problems in ren'ai games comes from the removal of intent. You decide the actions of the character, but the game decides why they did that there. It doesn't matter that you, as the player, have decided that you don't want to do something, like not killing the evil guy because you think he might not actully be evil. Nope. If the story doesn't fully support your action, you won't be believed. For all the illusion of control they give you, it's just little nudges here and there, and once you've sent your little mouse down one path, there's no turning back. The door's locked behind you.
...meh. My opinion? Ren'ai games aren't worth playing unless you have a strategy guide. The best intents in the world don't give you a snowball's chance in hell of actually getting a good ending, let alone hooking up with the character you're actually interested in.
I'm trying to figure out how I could possibly fix this and make a ren'ai game that I'd like playing - as a game.