If you've enjoyed Guardians of the Galaxy Volume 1 and Volume 2 then Guardians of the Galaxy Volume 3 will not disappoint. I would almost go so far as to call it the best in the series... except seeing the first movie for the first time is still one of my best memories of the MCU.
While it's not essential to the story if you didn't see the Guardians of the Galaxy Holiday Special on Disney+ it does kind of lead into and set up where the Guardians are at in Volume 3 quite nicely.
In this installment Peter Quill (Chris Pratt) is still not coping with the loss of his timeline's Gamora (Zoe Saldada) when suddenly the team is attacked leaving Rocket (Bradley Cooper) in a very bad way. From then on it's a race to save Rocket as we learn quite a bit about his origin in the process.
This movie is slightly darker than the first two and, if you're concerned about the animal cruelty that is causing some people to not want to see the film again, keep in mind, it's just a movie, and the fictional cruelty is what created not just one of the best CGI characters of all time in Rocket, but is also very much the same kind of cruelty Nebula (Karen Gillan) went through as well to be the person she is.
That said the cruelty is no more graphic than anything you've seen in a Marvel movie to date (Ant-Man's first solo movie for example) and, if you care about animal welfare at all, support a film that ultimately has a positive message for how we think about animals. It's the film's villain, the High Evolutionary (Chukwudi Iwuji) who is doing exactly what a villain is supposed to do - things you don't like and think are probably appalling.
To be blunt about it, the animal cruelty depicted here is nothing compared to some of the things that happen in any given action sequence to any evil character in any given superhero movie of the modern era... and you never hear any complaints when Star Wars characters routinely kill off giant native wildlife just doing its thing multiple times in a series.
I digress. It didn't bother me other than a few tugs at the heart strings and, as I said, this movie ultimately has a positive message for how people typically think of animals.
Overall I did enjoy the film. It has all the fun, action, humor, and heart you've come to expect from a Guardians movie and tells a coherent story with a satisfying end, that isn't just a place holder or set up for something that may happen in a future MCU movie.
If you've followed the marketing you may go into the film expecting it to end on a downer thanks to much speculation that one or more of the team may not make it through but I felt the film ended on a high note despite it being James Gunn's last as well as some of the other main cast members too.
My only real disappointment with the film is a bit of a double edge sword. On the one hand you get a more complete picture of Rocket and his backstory, which is great. However it comes at the expense of present day Rocket spending a good chunk of the film sidelined. As cute as young Rocket is, present day Rocket quipping and holding his own in an action sequence has always been a highlight for me of this series.
You still get plenty of Rocket action sequences. It's just this is the last movie in this particular series. I kind of wanted to see more of present day Rocket doing his thing. Not a major issue because it's also great to see so much of his past too.
If you've felt Marvel has dropped the ball with their last few outings (I'd agree with you) Guardians of the Galaxy Volume 3 is a return to Marvel at their best. Thanks largely to James Gunn having a clear vision for the kind of stories he wanted to tell with these characters right from the start.
Future Guardians movies have a high bar to live up to. Volume 3 may be the last time you'll see these characters written this well. It's certainly the last time you'll see the current roster in a film for quite some time, if ever (though never say never... right?).