I would say that it frustrates me when a game cannot decide what it is. You can't warn me about a boss one moment, then spring one on me without warning the next. You can't just suddenly start narrating out of nowhere like we haven't been through 20-30 hours of narration-free game. You can't present your game as if it has this cool "synthesizing" or item smithing system like it is this major feature for the game and barely have it in the game at all. Truly great games are somewhat consistent in the rules, relatively speaking. Baldur's Gate was brutal to the new player, to a point where it provided very little hand-holding after leaving the starting home 'Candlekeep'. But it was consistent. From the get-go, the player discovers that it is going to be that kind of game. Then there is Skyrim, which spoon-fed everything to the player. Items, characters, even entire adventures dropped on their lap with minimal player effort to thrust into them. Still it reasonably consistent in identity from beginning to end. And that is what a successful game does, it stays true to an identity from beginning to end. It's when games have mood swings and can't decide what the rules are. From game mechanics to storytelling. It's jarring when a JRPG suddenly wants to be a platformer or something after more than halfway through.