First the bad news - it helps a lot to watch the TV series before watching this movie. The bad news is that the word "series" is both singular and plural.
Obviously watching "The Mandalorian" is kind of a no-brainer. It's right there in the title. But unfortunately they didn't put everything into that series. They dumped some of it into "The Book of Boba Fett". It's unfortunate because that series isn't very good, in my opinion.
"The Mandalorian" season two ends with Luke Skywalker coming to take Groku for his training. Let me expand on that. A digitally de-aged Luke Skywalker - both visually and vocally. Season three starts up with Groku back with the Mandalorian. Err?
The answer to that riddle is in "The Book of Boba Fett". The dedicated one episode and part of another to just Mandalorian stuff. Short version is that Mado misses Groku, wants to visit him, and has a chain mail shirt made for him (out of the beskar steel spear he acquired in season two). Aww. The cloth it's tied into looks like Groku's head. He goes to the planet where he's being taught, gets talked out of visiting Groku, and leaves the shirt for him.
TBoBF also introduces the villains - a pair of twin Hutts who are cousins to the late, unlamented Jabba the Hutt.
Luke makes Groku choose between Yoda's lightsaber and Mando's chain mail shirt. The general fan consensus is that this is a dick move on Luke's part, given the relative time they've spent together and Groku's age. The episode ends with that, the next one has Groku arriving in a bot flown ship to Tattooine and Mando, wearing the shirt. Turns out Groku failed the jedi "No attachments" rule.
And that's how they get back together. Not a love story for the ages and they try to do the tear jerker thing but it doesn't hit. Season three is somewhat relevant because it shows Mando taking Groku on as an apprentice and formally adopting him, as much as it seems formal adoptions are done. Groku is now officially a Mandalorian apprentice. He's even got his own little beskar steel rondel he wears as a breastplate with the clan symbol Mando wears.
Movie time.
The brief review is that it's stuntmen in the armor unless Pedro is showing his face. They're fighting and interacting with mostly CGI characters against CGI backgrounds.
Anyhoo. On to the movie in a bit more detail.
Mando is now exclusively hunting down Imperial war criminals. He's hunting at the start of the movie. Many Stormtroopers meet their untimely/timely demise. Three AT-ATs are sent over the edge of a mountain while Mando and Groku run after his quarry on a kind of mechanical ostrich. Those things are seriously impractial with their high center of gravity and the ability to be taken out by damaging a single foot. But I digress.
This time the quarry is I guess brought in "cold", but they never show Mando going with the spatula to get proof of the job being done. Maybe they did it off screen but also the New Republic colonel who hired knew it was done messy but also didn't ask for any specific proof. Again maybe something handled off camera? Then again I don't remember him not bringing in his bounty "warm" in the series. Dunno.
She wants him to do another job. The combination of the two will get him a new ship - his beloved Razor Crest. He only gets the ship if he does the second job. He already refused payment on the first one, calling it a gift. Bad mercenary. Bad. The second job involves finding and returning the nephew of the Hutt twins. See that link to TBoBF? In return the Hutts will give information about the location of a known Imperial war criminal who has lots of information but has very little identifiable information to follow.
He takes the job. He meets the Hutts. They have an older picture of the nephew and it's an adorable baby Hutt hologram. Mando tracks him down as a really buffed pit fighter who's got one more fight before he's worked off his contract. He's also very aware that his cousins are looking for him because they need him very much out of the way to cement their place. This Hutt speaks perfect English (basic?) and just wants to make his own way in the world without having the specter of his father over his head.
Mando tries to buy out his contract and finds out that the fight is one where the kid is gonna die. Not might. Gonna. It's a type of fight where they keep sending opponents out until he's dead. Mando tells him this and while they're trying to break him out they're all gassed, Mando ends up in a cell, Groku ends up a bird cage.
I'm detailing a lot because this is where things are still kind of interesting.
Mando is tossed into the arena as the first opponent. The promoter had offered Mando a job as a pit fighter because he'd be a big draw, Mando declined impolitely. But hey. he's here now. Mando tells Hutt what kind of fight it is and the two of them work together to fight off all the creatures. Woo. They all escape and there's an honest to goodness speeder chase in the city.
Turns out Hutt knows what Mando needs and that the promoter is the Imperial war criminal. Now that he doesn't need the information from the Hutt twins he works with this Hutt to capture the guy. He brings the guy to the colonel, who then expositions that they had a deal with the Hutt twins and now Mando is in the crosshairs for skipping that step. Seems like it doesn't matter that the end result is standing there in cuffs. Seems like they're not willing to do a darn thing to help Mando after he got the results more quickly. Feels a bit .. how the Empire would do things.
Mando takes him back to his little farm he was given on Nevarro (assuming, not given any real reference for that one) and gets him a lift with a gunrunner he knows so Hutt can do his best to live his life and avoid his cousins.
Mado is captured by a bounty hunter (heh). Groku follows them in a ship with the little mechanics from season three. The twins have captured the nephew and are torturing him. They blame that on Mando, saying that they'd have given him a quick death if he'd done his part. Then they dump Mando into a pit pool filled with nasty creatures.
But first! They take his helmet from him! After all the crap he went through to atone for taking off his helmet they did worse and they knew it. I guess there's a loophole that it doesn't count if everyone who saw him is dead.
Nasty monsters. Fight scenes. Pedro's actually present in the movie. Groku and the little mechanics rescue Mando. But wait! Mando was bitten by the big monster and is now poisoned! Oh no!
He sends Groku off with the little mechanics and says he'll be right behind them. That's because the Hutts sent out a lot of their forces out to get him back. Mando goes off fighting until the poison drops him. At which point Groku pops up and tends to Mando, including healing the physical wound with the Force. Hence the "the old take care of the young, then the young take care of the old" stuff. Groku meets up with a CGI Cajun swamp dweller who can make an herbal poison remedy but - gasp - it may be too late.
Now I'll put in a bit that's meant to make people, mostly kids, laugh. Groku makes a mud hut for Mando and then uses the Force to push him into it. The helmet goes "boing" when it shows he's longer than the hut. Groku tries a few more times (boing boing boing) before covering his legs with ferns like he'd done earlier. Ha ha. Helmet go boing.
They use the battered gun runner's ship to storm the castle. Lots and lots and lots of mostly robot creatures fighting. Two big Warhammer 40,000 type terminators (if made by the Dark Mechanicum on a budget) guard the door. Groku gets inside and is playing with the wiring of one, making it random and damaging the other terminator. When they're both down he pops up and that's how Mando finds out he's still around.
They get in the throne room, more fighting. The bounty hunter that captured him gets a singlular fight. The nephew Hutt fights the twin Hutts. All three of the Hutts break through the grate into the pit pond. Groku uses the Force to lift nephew Hutt out of the pit pond. Yay.
A convenient save by New Republic ships, led by the colonel and including some of the characters from the series, takes out the entire compound. Mando, nephew Hutt, and Groku all survive. They go back to base, Mando and Groku take off, nephew Hutt decides to hang around and try to help the New Republic.
Honestly this thing couldn't have been tied up with a bigger bow.
On to the critique that I haven't already done.
One big issues is that there's no stakes here. We all know Mando and Groku are going to survive. We all know nephew Hutt will survive. All the good guy characters are walking merchandise opportunities. The only ones who die are the bad guys. The bounty hunter's dog-thing had taken one of the little mechanics and was playing with eating it but didn't. Groku gentled the thing with the Force when it was coming for him.
Something more subtle was that most of who got killed were faceless or Badtm. Storm troopers in armor. Robots. Fighting/non-sentient creatures. The Big Bad Guys (even then it's not quite confirmed that it's final). This was very kid-coded in that respect.
Knowing that Mando was mostly stunt performers and listed right after Pedro in the credits doesn't take away the sour taste in my mouth. Yes. I know. Darth Vader was acted by one performer and voiced by another so it's not new. It's just that giving him top billing when he's doing 99% voice work feels off. I've felt that way through the series too.
Groku is still cute and non-verbal. This time he's more proficient in things and him jumping around like Yoda was explicitly shown as part of his training by Luke. He's stronger in the Force too. They keep up the bit of him constantly eating, which still amuses me.
One big thing of note is that this movie excludes the female characters from both series. The only one is the colonel and even that role is minor. The series built up several good female characters but nope, they aren't given any consideration here. This has been very much noticed out in the wild.
A flat movie. Mostly CGI. No stakes. I'm not sorry I watched it but I have no plans to watch it again nor will it be on my movie server, taking up precious hard drive space.