This has probably been mentioned before. But the game play elements (rules) need more polish between releases. It gets frustrating and breaks immersion when there are small bugs in things like combat. Its nothing that can't be lived through, and is completely irrelevant when exploring new features, but once the newness wares off, broken game mechanics always makes me feel like I want to wait to play a later release.
The core of a simulation is its rules, if DnD had a broken mechanic, a game master makes a house rule to fix or tweak it. Blizzard updates patch to make sword X not so unbalancing, etc... With good mechanics, procedural content can last forever =) Even with few features. Take a non-procedural game like Quake, the rules are predictable, and well thought out. The game is still played today and has a huge audience. Simplification is not what I am trying to illustrate though. I am also not talking about balance. Just consistency and accuracy. Or predictability. A dwarf with a weapon should not die to a fingernail with infinite lives that delivers head-shots through the eye-sockets with 100% accuracy. Unless that is the intention. It doesn't seem so, it seems like realism is
*I think I should be clear to also say that, this type of thing should be able to happen, maybe 1% of the time, or it should have the same probabilities as lightening strikes or something* But when things break in this game, they tend to break in horrible freakish and insane ways
Wich is always fun the first time around, but the 4th, and 5th, not so much.
Fairness of the rules and game mechanics is probably a better term. Also the examples I used are just based off of what kind of bug would annoy me, no actual bug report going on here.