CGI is a controversial subject when it comes to Star Wars, and, while it's been used to the detriment of the franchise, it's improved it, as well.
CGI is really hit or miss within Star Wars. It either adds so much or takes too much away from the wonderful franchise. Many fans like the animated look of the prequel era, while others scorn the idea of CGI being adding in later to the classic films.
It's like Star Wars as a franchise is somehow known for both the clunky puppets and practical effects which are widely loved and known for their CGI characters, most of which have become giant memes. Even media released later, such as the sequel trilogy, tried to blend the idea of practical and CGI effects, while The Mandalorian has tried to be exclusively practical, such as Grogu being a puppet.
One of the main things that ruined the prequels and the special editions of the original movies was the fact that there was just way too much CGI spread throughout. While some of the practical effects of the original trilogy may have looked cheesy, they also were way better than the CGI effects added in after.
With the prequels, it seemed obvious that everything was done in front of a green/blue screen to add in the CGI setting. There was a very large disconnect from the actors and their surroundings that wouldn't have been the case had they had some kind of actual setting to mimic.
The force was definitely an added bonus that the CGI of the prequel era gave to fans. Before episodes one, two, and three, the force powers from the original movies seemed like the characters struggled to lift things.
This, of course, makes sense, considering Luke was still learning his powers, but, in the prequel era, the Jedi get to swing their sabers around, pull it towards them with ease, and jump around one another as they fight, making for some pretty cool combat scenes.
The scenes of Yoda fighting in the prequel era are extremely hit or miss for most fans. While kids and fans of the character may love to see the ancient Jedi swinging around with his much shorter saber, many fans felt like this slightly hurt his character.
Yoda was so much of a pacifist and was more of the "wise old sage" throughout the original trilogy that seeing him fight with a lightsaber made it seem like he couldn't just rely on the force. While it didn't hurt his character, it definitely gave fans a view of something they may have preferred to keep a mystery.
The combat scenes were definitely enhanced due to the CGI. In the original trilogy, many of the lightsaber duels were rather stiff and were heavily based on emotions. They took inspiration from old samurai movies and used them to the best of their advantage.
But, in the prequel era, the saber combat is a lot more flashy, which may appease many fans. The fight scenes are dynamic and use a lot more effects than that of the original, giving them an even deeper complexity.
This is one of the most unforgivable retcons of all time. In the remastered editions of the original trilogy, one of the worst edits made was of the first scene Han Solo appears in. At the cantina in Mos Eisley, Han shoots Greedo, killing the Rhodian bounty hunter.
Greedo never manages to get a shot off, but, in the remastered edition, he shoots first, Han slightly moves his head to dodge, and then retaliates. This change totally changes Han Solo and his personality, making him a bit softer than the scruffy-looking nerf-herder that he already is. Plus, as everyone knows, Han shot first—end of story.
Space combat in the prequel trilogy is pretty amazing. It is incredibly dynamic and seems to almost exclusively use CGI. In the original trilogies, they used a lot of models of different scales to shoot the big space battles, such as the Battle of Yavin on the Deathstar. But, in the prequels, everything is so much of a grander scale. Thanks to CGI, the space combat makes for some of the greatest scenes in the prequels.
The idea of adding CGI to the original trilogy is a pretty bad one, and many fans of the films hate watching the remastered ones because of this exact reason. The scenes are clunky and always looks extremely out of place, as the added in CGI isn't even that good. Other than the Greedo and Han scene, there is also an added Jabba scene in A New Hope that has Han walk over the Hutt's tail in the most awkward of scenes.
There is also Hayden Christensen, the actor behind Anakin in the prequels, that appears as a force ghost instead of the original actor. This isn't so bad, but many fans were pretty upset about this change, as well—not to mention all of the random creature add-ins to the films that look totally bizarre.
General Grievous was one of the coolest looking villains in the Star Wars films, and he was rendered entirely through computer wizardry. Everything about his design was impressive, from his face shield to his intense golden eyes. He also swung around stolen lightsabers like crazy and had a pretty amazing battle with Obi-Wan Kenobi in Revenge of the Sith. He was so well received that he went on to become one of the main antagonists during The Clone Wars series.
Jar Jar Binks was so hated that many claimed that the character single-handedly ruined the entire franchise, though, in recent years, he's earned cult appeal as a meme icon. But, original, Jar Jar Binks was the face of "CGI ruined Star Wars" as he was not only a goofy fool; he was also super annoying.
After Return of the Jedi, fans of the movies hated the Ewoks because they believed them to be a "cute" marketing gimmick. Well, that hate was revisited tenfold when Jar Jar first appeared. People hated him so much that the character ended up taking a huge back seat in the second and third movies, becoming totally irrelevant.
The clones first appear in Attack of the Clones and make for some of the coolest characters in the series. They are designed to look similar to Stormtroopers but are mass-produced and seen in dynamic settings going to war against the Separatists. These giant scenes are fully done in CGI and were the initial introduction to The Clone Wars series, as the clones became the most vital aspect of the show.