I'm afraid all my stories are quite tame by comparison to some of the gems in this thread!
In a rotating GM spot game, I left mid-way through a Demon: The Fallen game for a bundle of reasons. It's the only oWoD game I own, too, and was kinda psyched to play it at first. I'd sat through every other game in the group, as varies as Paranoia, Traveller, BESM and D&D, but this one was just too much for me:
- I told the GM I was specifically interested in playing Demon, not his other choice of Werewolf, because I'm not interested in the mainsteam oWoD or it's metaplot. Within five minutes of session one we're being spied on by a Vampire
and it's three or four weeks of Vampires, Vampires, Vampires before anything vaguely Demon-related turned up. This changed only because I complained pretty loudly that the game had turned into "Hunter, but with angel wings"
- Remember not caring about the rest of the oWoD? One other player knew the setting well and was in a PbP game with the same GM... and they would witter on, and on, AND ON at length about sometimes only vaguely related rules and fluff things. One of the better sessions involved a missing woman and a magical mirror, which was quite spooky and exciting.... and ruined when the GM and this player spent fifteen minutes talking about what magical powers from Mage could create it.
- Remember not caring about the metaplot? The game (ran just a year or two ago) was set in 1999, for basically no reason other than "It's an oWoD game and must be set in oWoD's present day". It added nothing to the setting over setting it in the present day; it was in fact occasionally a nuisance because we'd find, say, we couldn't quite judge stuff like internet use or mobile phone availability right when it mattered. I have no problem with setting games in period (I run an occasional 1989/1990 set Ghostbusters game) when it's part of the feel but it just felt like we had to hop on the oWoD train.
- The GM and his flatmate had very different tastes in games and the two of them would often bicker, especially as the flatmate was quite interested in juggling numbers and believed he could just tell when things were "broken" whereas the GM was more of a "I don't care about power levels" type. One particular fight dragged on when the two argued over whether a two dot power was actually better than the four dot version because of how it's worded.
- The GM, unlike every other GM in the group, sit at the head of the gaming group - he refused to sit anywhere other than His Chair to the side of the room. Every other GM could make eye contact with us all and hold the sessions better - he was positioned so that if he spoke to players on one half, he turned his back on us and we couldn't always hear him. (He's a quiet dude.) This forced repeititon and made it easier for players to end up nattering off-topic since they felt "out of the game".
- The GM would end every session by saying "Three sessions left." I wasn't enjoying myself and found the plot was flailing wildly but hung around because I thought an end was coming and that the game would finally tie into something satisfying. After abour six sessions of that, it was clear that it wasn't coming anytime soon - though he was known for being terrible at ending games so I should have guessed.
This is undeniably a case of me just not enjoying the game rather than it being dire, but I felt like I was being lied to and that if I'd had accurate info I would have said "no, thanks". When I expressed frustration at Vampires getting essentially top billing in a Demon game I was told "it's oWoD, crossovers happen, suck it down" by the GM and the oWoD-fan player - to which I argued that's like me asking people to stat up characters for a Batman game and then running session after session about The Haunted Tank, Darkseid and Sinestro. Sure, it's canonical, but that doesn't stop it feeling like false advertising.
Eventually I realised I was getting so pissed off wiht the game that I was in danger of being a problem player - That Guy who obviously doesn't want to be there and saps everyone else's enjoyment - so I left. He was a bit bummed.... and promptly ended in three sessions.
I went back to the group after that for a few blocks. I think me leaving took the wind out of the GMs sails because he said he wasn't going to run again for a while, except perhaps a one-off.... which I was quite interested in, especially because his obsession with huge arcs would make running a one-off an interesting challenge.
When his turn came up again and he said he was in fact going to run another campaign, I bowed out. There were other issues - cost and time of getting there and frustration with some other aspects of the group - but that particular GM was definitely a factor.