Sheik has been called a one-trick pony in Brawl: she has a great forward tilt lock that single-handedly dominates some matchups but otherwise is a mediocre character with some good gimping tools.
Forward tilt has been revamped into a more damaging but less locking version that has a more balanced effects on different enemies. To make up for this and give Sheik the overall improvement she needed, significant upgrades were made to her jabs, needles, and a few other key moves. She and Zelda also share faster transformation times so she can make better use than ever of her other half.
Either way, Sheik’s damage potential is faster and more relentless than ever!
Balanced Brawl Bonus: Rapid Strikes
Sheik’s jabs all have less ending lag. Her rapid jab in particular also does extra shield damage.
Other Major Changes
Forward tilt does more damage but is less of a locking move.
Down tilt and dash attack hit in a more favorable way.
Forward smash is less powerful but now reliably links.