Well this is tough because in certain cases it's very difficult to rate the acting performance separated from the writing and the quality of characterization. But here goes...
THE FORCE AWAKENSMark Hamill (Luke Skywalker) - 6/10 = It's not his fault. But even though his presence and facial expression nailed the scene and had gravitas, I simply can't give a high score to a cameo devoid of dialogue.
Harrison Ford (Han Solo) - 9/10 = It's amazing that Ford's acting on this character is always some of the best in every film even though he never found the character gratifying.
Carrie Fisher (General Leia) - 8/10 = slightly less better than Harrison but solid.
Daisy Ridley (Rey) - 7/10 = A good performance but I have to take off 1 point for her monotone "dear in the headlights" expression for almost every strong emotion she portrayed. And 2 points for writing and characterization issues.
Adam Driver (Kylo Ren) - 9/10 = His acting wasn't a problem. But I can't ignore some poor writing surrounding his character.
John Boyega (Finn) - 5/10 = His acting could've been worse. But he pays the price for being Jar Jar 2.0 when the storyline kept trying to tell us he was a prototypical rogue Stormtrooper.
Oscar Isaac (Poe Dameron) - 9/10 = There's a few writing nitpicks behind his character but he nailed it.
Andy Serkis (Supreme Leader Snoke) - 10/10 = He certainly nailed what he had power over in the performance of the character - a deep, sinister voice with gravitas.
Domhnall Gleeson (General Hux) - 6/10 = His speech was a little over the top but memorable. The rest of the time he was a pencil pushing knockoff of Tarkin, and not a very good one.
Gwendoline Christie (Captain Phasma) - 3/10 = This character was a hyped joke. A protocol droid in a chrome Stormtrooper outfit. The lines read like it and the acting felt like it.
Lupita Nyong'o (Maz Kanata) - 9/10 = I'm still not sure about how I feel about this character. But at least in TFA she served her purpose to the story. And Lupita voiced the character well.
Anthony Daniels (C-3PO) - 2/10 = The worst C3PO portrayal of all the episodic movies. And that's saying something considering how unnecessary he seemed in ROTS. Pathetic lines: "I suppose you want to know how I got my red arm?" Translation: you the viewing audience should ask. Then run to your local toy store and buy this version because see, it's red and it's never been red before! Also his comment to BB8 suggesting that R2D2 having the rest of the map is stupid when just the opposite is true. Utterly dreadful!
Jimmy Vee (R2-D2) - 4/10 = His plot McGuffin cameo felt contrived.
Peter Mayhew (Chewbacca) - 10/10 = Chewbacca was authentic enough, even though his instant fawning for Rey felt like part of Rey's MarySue recipe.
Max von Sydow (Lor San Tekka) - 10/10 = Very memorable cameo.
Simon Pegg (Unkar Plutt) - 7/10 = Meh.
ROGUE ONEFelicity Jones (Jyn Erso) - 9/10 = She could've brought a little more character to her character at times would be my only criticism.
Diego Luna (Cassian Andor) - 8/10 = Solid performance even though he was involved in a few scenes where the movie dragged a little.
Ben Mendelsohn (Director Krennic) - 10/10 = He totally nailed the character. Spot on.
Donnie Yen (Chirrut Imwe) - 9/10 = The character felt a little cliché at times would be my only criticism.
Mads Mikkelsen (Galen Erso) - 9/10 = Solid performance.
Riz Ahmed (Bodhi Rook) - 8/10 = He played a different kind of spy/defector - anxious and aloof. But the portrayal was good.
Jiang Wen (Baze Malbus) - 10/10 = I really liked his portrayal of this character.
Alan Tudyk (K-2SO) - 10/10 = He nailed the voice performance, which is a credit to him considering his character is not as animated a droid as C3PO.
Forest Whitaker (Saw Gerrera) - 9/10 = Believable as the stir crazy, battle weary leader of Rebel radicals.
Jimmy Smits (Senator Bail Organa) - 10/10 = He picked the character up where he left off in ROTS. And you got the sense that he had been hardened by the Empire's oppression over time. It's one of the things that made Rogue One feel like a bridge between ROTS and ANH.
Genevieve O'Reilly (Mon Mothma) - 10/10 = Another solid performance in the character.
Alistair Petrie (General Draven) - 7/10
James Earl Jones (Darth Vader) - 9/10
Guy Henry (Grand Moff Tarkin) - 10/10 = Incredible portrayal even though some people nitpicked the CGI.
THE LAST JEDIMark Hamill (Luke Skywalker) - 8/10 = His acting was great! But I have to deduct for the poor characterization by the writers.
Carrie Fisher (General Leia) - 10/10 = The Mary Poppins in space scene aside, it was a fine farewell performance.
Daisy Ridley (Rey) - 8/10 = I thought her acting slightly improved. But the writer(s) did little to develop her character outside of her Force flirtation with Kylo.
Adam Driver (Kylo Ren) - 9/10
John Boyega (Finn) - 7/10 = Better, but still hurt by some of the writing. Ugh!
Oscar Isaac (Poe Dameron) - 8/10 = Not his fault but some of the writing surrounding his character. Bad.
Andy Serkis (Supreme Leader Snoke) - 10/10 = Even better than in TFA. Too bad they built so much intrigue around character who was a throwaway.
Domhnall Gleeson (General Hux) - 3/10 = Just dreadful! He was like a Jar Jar Binks version of his TFA self.
Gwendoline Christie (Captain Phasma) - 4/10 = She finally gets some action. But it was slightly better dialogue and slightly more screen time. Plus it was hard to miss some of the contrivances in the scenes surrounding her duel with Finn. Hopefully this character has finally been put out of it's misery.
Laura Dern (Vice Admiral Holdo) - 6/10 = Ugh! Writing!
Benicio Del Toro (DJ) - 5/10 = He captured the character. It just wasn't much of a character.
Kelly Marie Tran (Rose) - 6/10 = I'm still trying to figure out how I feel about this character. "Meh" at this point. I suppose her acting was okay enough.
Frank Oz (Yoda) - 6/10 = His voice was as good as ever. But sorry, I found this to be worst Yoda characterization ever. Book burning party/conga line party Yoda is not for me. I thought after he wacked Luke on the head with his stick, he was going to hold it up in the air and start limbo dancing under it!
Anthony Daniels (C-3PO) - 7/10 = More cameo duty. But at least he came off natural and wasn't an embarrassment of a portrayal like in TFA.
Jimmy Vee (R2-D2) - 8/10 = His "bonding with Luke" cameo was great.
Joonas Suotamo (Chewbacca) - 8/10
-------------------------