Quite a few.
Gran Turismo, this has been among my all time favorite franchises since the early PS1 days when we rented the first game every weekend, but on PS3, the series seemed to stagnate and even move backwards. They removed features and customization and kept on using ancient meshes, textures and vehicles, their physics models and sound design has also severely lagged behind other franchises for quite some time. GT5 was quite disappointing, GT6 was very disappointing, it seemed to want to be an online game first and foremost, menus were more difficult to navigate than ever before, sound as bland as ever for most cars and the same screeching rubber SFX that followed since GT3 on PS2, they didn't even try with new tracks and some old and dear ones have been removed. To make matters worse; the last two iterations took a long-ass time to make, time that seems not to have moved the series forward at all and it's super annoying for an old fan who's played these games since age 12.
Metal Gear Solid, it was obvious that it would go downhill when Kojima left, but I started losing interest before that as well. It's simply to contrived and over-the top at almost every junction and the addition of ridiculous real money online bullshits in MGS5 really made my blood boil. Gameplay hasn't really changed much either in almost a decade, the series needed a renewal, but now it'll be sent out to the pastures to die an undignified death.
Need for Speed, these games used to be awesome and then the Underground era started, quickly followed by "plots" and then followed by at least 4-5 iterations that were exactly the same rehashed bullshit with no value and a thirteen-on the dozen soundtrack that people like for some reason. The Fast & the Furious movies are partly to blame for the butchery of the series, but stupid customers just as much. Criterion's attempt was a decent one, but other arcade racers had already showed the way and it was rather unimpressive from the geniuses behind the Burnout series.
Call of Duty, the first two are still among the best shooters I ever played, they set a new industry standard for pacing, frenzied narration that focuses on immersion before plausability and it also triggered the team shooter mechanic in earnest. The third one was not very good but then came Modern Warfare, and it was brilliant, almost as genre-defining and brilliant as the very first one, and this is right around the time where it became a massive commercial success, which happens to be where the series started losing its way. I've tried a few of the later games, but they're uninspired, lazy, technically unimpressive and seem to exist solely for the purpose of knowing where all the western world's foul-mouthed pre-teen boys are at all times.
Final Fantasy, I honestly haven't played any of the ones before FFVI, but found VI, VII; VIII, IX and X to be utterly fantastic. X-2 was the series' first proper stumble in my opinion, it was way too childish, unengaging and mostly felt like a cheap cash-in on the immense success of the previous main game. The online attempts only shows that Sqeenix want the same dollars and yen that Blizzard have more or less confiscated from the industry at large since the release of WoW, and both FF online games are seriously underwhelming to me. FFXII was a high point in the series for me, I truly enjoyed it, perhaps even loved it, it was back to being cheesy in a charming, campy way, and the pacing was quite good, the story is even decent and the combat was awesome, the hybrid system was great, in my opinion. Then FFXIII arried and I knew that the series would never come back for this disaster; this is the most disappointing generational transition of any franchise I've ever played, the game literally does not have a single redeeming quality compared to the previous greats and the "combat system" is the worst turd I've ever had the displeasure of accidentally stumbling into. Pacing is shit, characters are the weakest ensemble ever in the series, combat is beyond terrible, the score is utterly forgetable and the setting and exploration are completely worthless, sprinkle that with painfully bad voice-acting with none of the campy charm of FFX and an extremely linear first half of the game and you have yourself a contended for biggest letdown in the history of gaming, for me at least.
There are more series that I've stopped liking for various reasons, but enough negativity for now... 
Currently Online 
