In a nutshell
Bowser is the heaviest character in the game, but also has the largest hurtbox, which means he'll get hit really easily. Bowser is your typical heavyweight, sluggish but powerful. Bowser received a useful new tool in Brawl, which is his Flying Slam. Bowser also has great frame advantages when grab releasing which helps lead into his finishers, and he can regrab anyone except Donkey Kong after a ground release. His Whirling Fortress makes a great out of shield move and has good knockback. Bowser relies on his good-ranged jab and tilts while on the ground, and has a surprisingly decent air game with his Flying Slam's second jump refreshes coupled with his powerful and ranged Fair. Currently, Bowser is 32nd on the tier list for Brawl, in the "G" tier, a slight improvement from his bottom tier position in Melee. Although he has received some good buffs, his mediocre tournament results, very low vertical recovery, vulnerability to infinite chain grabs, and near terrible match-ups nevertheless leave him in the G Tier.