Liam Neeson, Ewan McGregor, Chistopher Lee, the overall art direction, and Liam Neeson.
Seriously, say what you will about the prequels, but you simply have to admit that they're freaking beautiful, 'specially compared to the original's blander than a blandy Sammich with extra Bland sauce visuals, and I find that the soundtrack is superiour to the original trilogy's is. Seriously, The 'Imperial March' is the only theme worth remembering from the original, while the PT's have such beauties as 'Duel of the Fates' and 'Clash of the Heroes,' along with the ambient music in general.
Beyond that, the aforementioned Battlefront 2 and Republic Commando games, neither of which would have existed without the prequel trilogies. From what little I've seen of it, the Clone Wars is alright, but I haven't seen enough of it to judge it fairly.
Also, did I remember to mention Liam Neeson?