TLDR: The movie is essential a propaganda-ised copy past of Top Gun. However it has really good cinematography and CGI along with casting and acting
Most of the comments giving this movie any good comments are by people who are blindly patriotic and have surrounded themselves by anti-Pakistani/pro-Indian propaganda (Source: I'm an Indian who isn't blinded by the propaganda). The cinematography itself is really good, along with the CGI. This movie is fine to watch if you turn off logical thought for those who aren't prone to propaganda/have watched Top Gun and/or know a thing or two about planes.
First and foremost, a good chunk of this movie is Top Gun. From characters to scenes to even props, anyone who's seen Top Gun and is a huge fan of it like I am, can see this is a copy. Patty, the main character, rides a motorbike and is somewhat defiant to orders from above, if only that resembled Maverick. The first half of this movie is essentially just scenes from Top Gun and Top Gun: Maverick. In some scenes they at least change where they are when they shoot the exact same thing that happened in one of the two Top Guns.
Secondly, the film is basically full of propaganda. Indian films are known for their insanely unrealistic fight scenes, but in Fighter, they serve one purpose, not plot armour, by propaganda. The main purpose of the second half of this movie is to make reinforce the idea that Pakistanis are the eternal enemies of Indians. There's a couple of times where Pakistanis are humanised, but for the most part they're depicted as bloodthirsty animals, and Indians as the only decent people in the entire world. Also, if you've ever seen a Russian/Chinese film and saw "damn there's so much propaganda in this" be prepared because Fighter will bring you to a new low.
Thirdly, the movie heavily glorifies war and sacrificing your life for your country. I think being patriotic is great, but movies like Fighter take that too far. A lot of Indian movies which have plots that revolve around the hostile nature of Pakistani-Indian relations for some reason glorify death in war. I would love it if there were instead movies released which did the opposite, show war as it truly is, brutal and full of suffering.
Fourthly, Bollywood was most likely aiming to have the affect that Top Gun had in America, substantially increase the amount of applicant for the air force and navy. But unlike Top Gun, Fighter is not based off the story of real people, who did things most pilots would deem impossible. However given that this film is made to appeal to a mostly patriotic and blinded-by-propaganda audience, they don't need to show realism.
Finally, the production team have no real knowledge about the air force, terminology or anything really. If a film like this was made for a Western audience, they would be tearing the movie to pieces with how inaccurate it is. Top Gun and Fury, two of the best known US military movies, have amassed so much hate for minor inaccuracies, if those same people were to watch Fighter, they would probably kill the production team and protest against the IAF for allowing a movie this inaccurate to be aired. The movie contains so many inaccuracies, it's a miracle that the IAF did think that it was ok to let it hit the cinemas.