I'm mixed with my feelings on Sport, but I'm leaning heavily towards Sport ruining the franchise.
The pros: Online racing. A large player base means well populated lobbies in daily races, which other sims struggle to even get close to. The strong emphasis on sportsmanship and E-Sports has made me into a much faster and safer driver than before. The fact that car settings are locked for almost all races means that people don't have to spend centuries finding an optimal setup for each event, and that pace is dictated entirely by skill. The graphics are gorgeous as usual, and the game sounds pretty good for the first time in the series. And in the GT6 days, if you told me Gran Turismo would allow you to customise your cars with license plates and liveries, I'd have laughed at you. Right now, the livery editor and the user generated content is easily half the fun of the game.
The cons: The AI still sucks, which means this game offers zero enjoyment offline in Single Player. The campaign races feel more like a chore than an achievement. The entire road car classification system is a terrible, tasteless joke. The credit economy is horrible. The tuning is stupidly simplistic. All of this can be forgiven if online racing was solid, but unfortunately, PD seems to have given up entirely on the penalty system after years of not getting it right. Consistent glitches such as the grid start bug, pit bug, FIA disconnections, the penalty system, and unfair SR drops and DR resets make Sport Mode feel more like a stressful job than fun for me, someone who's not an alien. I really applaud Kaz for not resting on his laurels and wanting to make something really different, to bring the franchise, and perhaps even racing sims as a whole, to the next level. The World Tours are all amazing to watch. I just wish the execution of it was better, and that there's more content for an average skilled person like me to enjoy.
Overall, GT Sport just feels... empty, to me. I don't look forward to booting it up at the end of every day at school or work like I used to with the older titles. It hasn't the charisma or charm of the older, more content rich titles. Sport Mode feels like it only rewards the top few World Tour material players, and no one else, whereas I can still boot up GT6 and spend hours on it running time trials on my own, testing different cars across vastly different tracks, tinkering with settings, etc.. I think Sport has shown me that I'm more of a casual racer than competitive, which may explain why I find Sport so unfulfilling.
The deepest impression Sport has left on me is unfortunately a very negative one. I bought a PS4 even before a Gran Turismo game was announced for it, just for Gran Turismo. I bought a Logitech G29 specifically because it was compatible with both the PS3 and PS4. To me, Gran Turismo has always been a constant in my life, and thus buying each instalment was a no brainer. During the open beta and at launch, the FFB and tyre models were so horrific for road cars I couldn't even drive a Mazda Roadster around without crashing. The game was empty and buggy. The final product felt like an open beta. I was so disappointed in it I almost gave my copy away to a friend. While those issues have been addressed via updates, each update kept me entertained for about a week before I ask myself, "okay, so what? What's next?" My faith in PD and the series has been shattered by GT Sport. I'm cautiously waiting for reviews of GT7 before I buy, and if the AI and penalty system still remain garbage, I'm probably not going to support the series any more.