Everything a sequel needs to be, quite simply bigger and better. Sucker Punch's style is found at its very best in Sly 2: the characters you know and love are given so much more personality in design and dialogue; the world is expanded and can be explored to great depth; there are many additions to gameplay mechanics such as pickpocketing and paragliding (which is awesome) and it never feels repetitive or frustrating in the same way the mini-games of its predecessor do.
I've loved the Sly games since a young age but never quite knew anyone who'd even played them - they can keep their Ratchet & Clanks and their Jak & Daxters because Sly is simply the best of its kind.