mmm, I'd have to disagree with everyone then.
The CGI in Revenge of the Sith is for the most part, exceptional. It has some dodgy moments for sure, usually involving the over exaggerated movement of a Jedi or organic life form. It's easily one of the best films in recent times as far as image quality, sound and special effects go.
The practical effects in the original Star Wars are also exceptional and hold up well, but let's not kid ourselves on here.
A blend of CGI and practical effects obviously offers the best of both worlds. There are some scene's which have to be used with CGI if the director wants his vision to be portrayed on screen, they just can't been done otherwise.