I mostly play 3 medium classes: Soulbeast, Scrapper, and Daredevil, so this one affects me personally.

Initial reactions:

• The change to flanking makes Hunter's Tactics in Skirmishing a straight 15% damage increase on a minor trait. Selfishly, yay? But it feels kinda cheap, and it essentially eliminates a key skill tactic.
• The changes to Speed of Synergy and Kinetic Accelerators is a bit of a gut punch for my Scrapper. Way less application and duration for the only rare group boon (superspeed) I was bringing to the table, and the added reliance on Hammer 3 means I'll be flinging myself off cliffs with greater regularity as the zerg kills targets before the skill procs. Also, the Function Gyro made a lot more sense when you could save it for when you need it as opposed to becoming an integral source of blast finishers in the rotation
• My bounding-power-staff Daredevil got increased damage, but only in PvE. I guess that's okay because he's too squishy for me to play anywhere else. I like that they completely reworked the Acrobatics trait line, as it was in a really bad place, while random stolen skills were nerfed. I'm not sure this makes it worth taking over Trickery, but I guess we'll see.

Overall, these look to be pretty impactful to my personal gameplay. I'll really have to actually see how it feels in-game, but I'm fairly confident that I will not be able to ignore this change.