As for the movie itself:
I didn't mind the liberties they took with April. I thought it was an interesting move to make her an aspiring journalist and the same age as the turtles. I thought it was a little odd that Bebop and Rocksteady fought alongside the turtles against Supafly since they are predominately the chief henchmen for Shredder. For the purposes of the story, it made sense for Supafly to have a mutant family as opposed to just being a mutate form of Baxter.
I loved seeing them as proper teenagers and it was a great touch to voice them as teenagers. The turtles are all supposed to be like 15, so them wanting to watch movies, stay out late, experience high school, and chase girls was all on point character-wise.
The one change that caught me off guard was Splinter, and I'm not sure how that will work with Shredder. In the cartoon, Splinter and Shredder were rivals. Shredder chased Splinter to NYC, and that's where Splinter found the turtles and was mutated into a rat. That why Splinter knew martial arts to teach the turtles, and that's why Shredder and Splinter have this vendetta that drives a lot of their interactions. I think story is slightly different in the comics (i.e., Splinter is the pet rat of the master that Shredder fights), but the essence is the same. Making Shredder some kind of a mercenary is a weird take.
That being said, I really did enjoy Splinter's storyline and how they portrayed him though. Jackie Chan was a perfect casting.
I am not about to call this a "great" movie by any stretch, but it was really fun and entertaining. Solidly a "good" movie. I loved the way it was drawn as well. Between this, Puss in Boots, and Into the Spiderverse, I love the way they are doing these animated movies now.