Coming back to GW2, what's changed with Engineers?

I took an extended (like 2 years unfortunately) break from the game and have recently had a severe itch to get reacquainted with the game. What's changed about Engineers that I should know about before popping into some PvP?

Ugh.... picked a bad time to ask that question. Depending on what mechanics were around last time you played, Scrapper's entire spec got pretty heavily messed up in the last update. Both sustain and Damage suffered varying levels of nerf (and all the traits scrambled), and the F5 skill is now the function gyro that has all the old problems of the original Gyro, BUT now also took way the Elite Tool belt slot.

Holo's biggest change is overheating kills your tool belt entirely. A secondary change was the Heat related damage bonuses now scale as a coefficient rather then a set of Tiers. Most other skills still go by tiers, so its almost a non-change.

Core Engie still kind of sucks.

The build sites are still sorting through the mess, since every class got some kind of incomprehensible concept tweak that hasn't resulted in any net positives for the class overall.