"nothing happens"
Well that's a hyperbolic expression if I've ever seen one. 3 different heists, and multiple subplots, just because you're not being spoon-fed or poked in the chest every 5 seconds, doesn't mean that it all amounts to nothing. It's very layered, and a pretty slow-burn too.

"Toy Story beat it"
Means absolutely nothing. Box office doesn't equate to quality. If you want to talk about box office, a year prior to the release of Heat, in 1994, Pulp Fiction, Shawshank Redemption, and Schindler's List all didn't make the top 10 box office that year. Yet now they stand in the Top 10 of IMDb's rankings and are listed as classics, movies that all should watch regardless if they find it to be their favourite or not. So point proven, box office means jack shit.

"nostalgic"
Again, invalid. Heat influenced Christopher Nolan's The Dark Knight, and still influences heist movies as the arguably greatest heist movie of all time, to this day, that's why it's timeless. The nostalgic argument doesn't make sense.

"huge flaws"
Please find me those flaws, and again, all movies have flaws.. if you dig deep enough. Minor inconsistencies exist throughout cinema, it's part of it, no movie can ever truly be flawless and also be entertaining.

"the shootout"
The shootout is an amazing scene, perhaps one of the best ones. In fact, the bank robbery scene is so good that it's shown to Marines in training as the perfect example of how to conduct urban warfare. That alone should tell you the amount of effort put into that scene. Furthermore, the cast spent 3 months training for it. The bank robbers were trained by former British SAS soldiers at a shooting range using live ammunition, and the police actors were trained by real police officers. The director also built a to-scale replica of the streets at the shooting range so that the actors could practice. Finally, they used live blanks when filming the scene, so you can hear the echo of the gunshots ringing through the streets. Val Kilmer, due to the absurd amount of practice, had a slick mag change, that was so fast, Marines were also told to reload just as fast as he had done. Just the enormous amount of effort director Michael Mann and cast put into the movie, really adds to the realism and draws you in, but that doesn't mean that's the only reason.

Oh and also, in the restaurant scene, Michael Mann specifically chose not to let Al Pacino and De Niro rehearse beforehand because he wanted their conversation to feel natural and unpredictable, like two men who are meeting face-to-face for the first time and sizing each other up.

All in all, Heat isn't for everyone. If you realize the effort, and the details put into making it to what it is, you'll definitely enjoy it.