Revenge of the Sith did have some pretty good epic set-pieces like the battle with Grievous, Order 66 in Kashyyyk, the destruction of the Jedi Temple and Anakin's moment of turning to the dark side.
My main grievance with RotS is that the build up of the character of Darth Vader in the movie didn't match up a lot with both the old trilogy and how they were portraying it in the new trilogy. They completely cast aside the whole "the one to bring balance to the force" profecy, the high chancellor/emperor Palpatine interactions were poor, given that Palpatine was supposedly leading him on the dark path (that wasn't well conveyed in the RotS, they did a better, much subtler job on Attack of the Clones) and the scene were Anakin snaps at Padme could have been done much better.
Current PC Build
CPU - i7 8700K 3.7 GHz (4.7 GHz turbo) 6 cores OC'd to 5.2 GHz with Watercooling (Hydro Series H110i) | MB - Gigabyte Z370 HD3P ATX | Gigabyte GTX 1080ti Gaming OC BLACK 11G (1657 MHz Boost Core / 11010 MHz Memory) | RAM - Corsair DIMM 32GB DDR4, 2400 MHz | PSU - Corsair CX650M (80+ Bronze) 650W | Audio - Asus Essence STX II 7.1 | Monitor - Samsung U28E590D 4K UHD, Freesync, 1 ms, 60 Hz, 28"