Pretty much the only thing wrong with Sly 2 is Clock-La is a pretty meh final villian. But even then, she isn't awful it's really only the name, so I overlook it. But the story, villians, the gang, the open world, the missions are all A .

For Sly 3, there are one or two meh levels, depending on who you ask. Specifically, Rumble Down Under. It isn't by any means the worst in the series, but out of the OT it's definately at the bottom with only one real standout mission at the Lemonade Bar.

So while yes, An Opera of Fear is phenomenal, and the rest of the episodes are good, if not great, Rumble Down Under takes it down a hair, plus add in the half finished gameplay style of Panda King, the Ship, and the downright unpolished RC sections you still have a game that is a solid A-.

Really, the only thing Sly 3 has on Sly 2 is Dr. M. Probably the best villian of the whole franchise, who has a really challenging boss level after a phenomenal parkour dungeon.

TLDR: Sly 2 has a A game with an A- final villian, while Sly 3 has a A- game, with an A villian. The game is weighed heavier than the villian, so sly 2 just barely edges out Sly 3. Both are still great though. Top 10 games for me.