I went into this movie after almost 10 years working in EMS, currently as a Paramedic in a decent sized city (not anywhere close to NYC though). I also read and enjoyed the book it's based on (Black Flies by Shannon Burke) which is fictional but written by a former FDNY Paramedic and set in the 90s.
I have to admit my expectations were low, TV/Movies typically gets the job wrong and EMS is usually sidelined to minor roles (but I guess that's true in real life, just ask and EMT or Paramedic how much they make compared to police or fire, and how well represented they feel), and book adaptations rarely can capture the entire book.
That said, I think this movie did a great job with it. The chaos on scenes, and how Ollie Cross grows from getting pushed around on scene to become assertive and do the pushing. The subtle way that Cross goes from new and visibly nervous on his first lights and sirens ride to a call, to how numb and toned out or focused and calm he is towards the end. The downtime of grabbing some food in between calls, the hazing and comments from his more senior coworkers. I think it's a realistic amount of character development for the timeframe the movie takes place in, and is pretty true to the book.
Some of the scenes were different from the book, and in the book his girlfriend is different. She's someone he knew from before working as a paramedic and they grow apart due to him getting sucked into the job that was supposed to just be a stepping stone to medical school and becoming more jaded and burned out and losing that overt altruism of wanting to save the world. She's somewhat limited in the book as well, but it would've made for a better character than just providing mostly nudity and sex scenes. They also severely limit the character of Verdis.
The job isn't all high paced cardiac arrests, overdoses, and gunshot wounds and the scene of telling the presumably homeless woman to get out of the Laundromat did a decent job showing the other side of the job that doesn't typically get any attention. If it were fully realistic to the job, it would've made for a pretty boring movie of handling medical calls that aren't life or death emergencies, so I understand why it's more "action packed".
I won't spoil it, but what happens with "Rut" is pretty accurate to the book, and the ending of the movie is pretty close to the ending of the book. It just sort of ends shortly after the spoiler I won't mention, (though it ends a little different in the book) and leaves you feeling heavy.
The medical procedures and terminology was also surprisingly good for a movie, some things I understand can't really be performed due to working with actors, like you can't fully stick a laryngoscope down and awake actors throat, or do full chest compressions, so I won't fault that. I've seen much worse medicine in movies, and for me it can really destroy the immersion and realism.
Visually I enjoyed the movie, I've never been to NYC but the lights, sounds, and dirtiness of where a majority of EMS calls take place was accurate. The special effects for blood and wounds looked pretty accurate, and some of the details like sweat were good, though usually people that have lost that much blood who go into cardiac arrest or have a respiratory emergency are much paler/bluer. I thought the acting was good, I'm not the best at picking out why acting is good, but the main characters seemed convincing enough and not completely off from the book characters.
I'd probably give it closer to 4.5 stars, just a few differences from the book that I think would've made it a better movie and made the message get across a little better.