We get to see two large and dangerous cyborgs; General Grievous and Darth Vader. Grievous makes most of the common battledroids look harmless and incompetent, although he seems little more solid himself; perhaps the main difference lies in the speed with which he moves.
Force telekinesis seems to have reached its popular height in this film, and is used extensively in combat. As a point of reference, moving a one ton object upwards ten meters or so takes ~100 kilojoules under standard gravity; Yoda and Palpatine easily are seen invoking many megajoules of expended Force energy during their fight - and then throwing around lighting and dueling like madmen. Quite a remarkable showing. Darth Vader's undirected telekinetic display at the end of the film is also intriguing.
There seems to be a very dramatic difference in the capabilities of different kinds of Jedi and droids; while Mace Windu's showing against Palpatine is quite impressive, his companions on the mission to take out Palpatine are not apparently as dangerous. R2D2 is capable... and line battledroids are about as incapable as we could imagine, possessed of little strength, reflex, or skill.
Apparently, Obi-Wan learned the value of waterproofing his lightsaber after the incident in TPM (cut from the cinematic edition of that film.)