Low Slash is probably my favorite heroic encounter power in MP. Its been 3 game sessions since Ive traded my other lvl3 encounter for it, and I have already used it far more then the Bait and Switch since it is less situational. Getting 4 attacks in a round (Standard:Knockout, action point:Other big power, minor:Critical of opportunity, Move as minor:Low Slash) has been very powerful so far. More so because of Action Surge and Slaying Action.
Sneak in the Attack is a great damage utility for focus of fire if you have a target surrounded, and Gap in the Armor is a +2 to hit for the entire encounter vs one target a day. Excellent for Solo creatures.
Some of my other favorites are abilities that add extra actions into the mix. From the Shadows and Escape Artist's Gambit as an Artful dodger add a LOT of extra movement. Guerrilla Blitz lets you move your speed and adds to your AC and Reflex for it, allowing for great hit and run tactics.
At first glance a lot of powers looks fairly simple, but rogue powers all share one common facet, they are less about pure damage and more about Damage plus Utility and/or Effects. Overall, MP adds quite a few viable powers to the mix for a Rogue, and a great deal of interesting themed powers.