Sly 3 may not live up to the others, but it is still a very good game all around.
The Cooper Gang has grown after the events of Sly 2, in search of a vault made by several members of the Cooper family from the past that a mysterious villain called Dr. M is trying to break into himself. Sure, the original cast (Sly, Bentley, Murray and Carmelita) are all here with a past villain making a surprise reappearance AND two more from the first and second game respectively end up HELPING Sly in the long run, but the newer cast don't have the same charm or charisma that they have and above all that, they feel completely out of place. That is the one thing that really hurts Sly 3 in my opinion.
Gameplay wise, Sly 3 plays almost identically to Sly 2 but with some minor tweaks. You still have the open world to venture around and do jobs that ultimately lead up to the big heist. From the country of Italy to the snowy mountain region of China, each level is cleverly designed to suit everyone's respective specialties. One major tweak is, well, pick pocketing. In Sly 2, the only one that was able to do so was Sly Cooper himself. Now, Bentley and Murray are into the act though their methods are a tad bit more creative. Bentley uses a magnet to lure out whatever they have hidden in their pockets while Murray uses a more physical approach and heaves them over his head while shaking them into submission.
Along the way, pick pocketing certain enemies will bring up a new item that can be sold and the spare change used to buy upgrades for the gang. These are not necessary to beat the game as Sly 3 is pretty easy to beat, though some of them do help in the long run.
New to the series? The ability to play as Carmelita Fox. Up to three times will you play as Sly's nemesis. Gameplay as Carmelita is reminiscence of a light gun shooter with strafing and some platforming. She can lock onto a target and whilst doing so, can bop and weave to avoid retaliation from enemies and an extended jump that sends her straight into the air, making jumps that neither member of the Cooper gang can pull off on their own, especially Sly. It's a shame that you don't play as her for long, as Carmelita segments are one of the better installments to this game.
After completing a level, you unlock various challenges as well. They are all completely optional and are all easy. Some may require some more practice to successfully finish them, though none of them are painstakingly hard to do.
Sly 3: Honor Among Thieves still have the charm that have made the Sly Cooper franchise special. Though, with little to add on to the game and a lackluster amount of new characters, this could be one of the weakest of the three games.