After the travesty that was the Phantom Menace and the long winded mediocrity that was the Clone Wars, thank God Lucas managed to get something down on film that didn't make you want to punch him to square on the nose and just slap him about the face a bit.
You'll still find annoying, childish, stupid jokes slipped in there - but thankfully not on the same scale that they appeared in the Phantom Menace. You'll still find 10 second cut scenes of ships taking off, and others that are pointless and add nothing to the story but again, thankfully not on the same scale as in the other prequels.
The action sequences are handled a little better too. There is still blatant disregard for the laws of physics and reality but they do at least look much more impressive; although some of the effects are still too over the top and look fake as hell, with human actors and CGI being moulded together less than seamlessly.
Putting aside an overuse of CGI throughout, at least some of the acting is better (although much is still terrible) and McGreggor seems to handle the role of Obi-wan better than before even though he is still totally wrong for the part. Overall, Revenge of The Sith is still not great, but it does feel darker and a lot more Star Warsy.
Luckily, mainly due to The Emperor who is brilliant and menacing throughout, it at least ends the prequel trilogy on a note that slightly resembles the original films. There is still lots wrong. It's too long, the dialogue is still terrible, it's full of plot holes and, well I could go on, but it is watchable without experiencing the totally deflated feeling and utter disappointment that the first two prequels leave you with.
It's like someone sat Lucas down and gave him a long stern talking too and told him what was what... Then he still threw his toys out the pram, screamed and kicked and they eventually came to a compromise that was still pretty rubbish and Lucas filled with crud, but the rest of the team managed to lend it at least some credibility.