Despite lacking Sly 2's creativity Sly 3 is a great platformer by any standards.
The story is that after the defeat of the Klaww Gang at the end of Sly 2, Bentley is confined to a wheel chair and Murray, blaming himself for Bentley's accident, leaves the gang. Soon after that Sly finds out about the Cooper Vault, the final resting place of the fortunes of every one of Sly's ancestors. The vault, hidden on a small island has already been found by Dr. M, a mysterious villain who has tried to open the vault for decades without success. In order to get past Dr. M's enormous security, Sly has to not only re-recruit Murray but also recruit other members, each with their own thieving specialities. Sly 3 definitely doesn't have as good of a story as Sly 2 which has a story with much more continuation and tons of plot twists but it's still decent enough to end the trilogy.
Sly 3 has the same formula of Sly 2 with playing Sly and his two friends through a couple of episodes and playing multiple sub-missions before playing the final mission in each episode. In each episodes (save for the last one) you'll be trying recruit a member for the gang, always with something getting in your way. Sly 3 is slightly shorter than Sly 2 with only 6 episodes instead of 8 and fewer missions in the episodes. Sly 3 however makes up for it with a much bigger replay value. You can still buy multiple gadgets but this time the main replay value are the Master Thief Challenges which are either old missions but under either a time limit or with only half a health bar or it could be a brand new challenge.
The most exciting part of the game has to be the playable characters. Instead of just 3 playable characters (Sly, Bentley and Murray respectively) the gang is joined with 4 new members: The Guru, Penelope, The Panda King and Dimitri. Along with them you can also play as Carmelita, the cop who chases you through the entire trilogy.
The best part about Sly 3 has to be the enormous variety. Other than the regular platforming missions you can also control remote controlled vehicles, drive an airplane, dive underwater, shoot fireworks, go into disguises, control the minds of enemies and sail a freakin' pirate ship!
So i'll end this review by simply saying that Sly 3 isn't as good as Sly 2 but is still a truly fantastic game with tons of variety and a worthy end to a masterpiece trilogy.