The Metamorph league hit Path of Exile with a great amount of buffs and reworks to many Bow bases along with changes to many of the Bow skills. Some of the old strong builds retained their power, though, and are still perfectly usable.
We can definitely say that summomers are one of the most solid choices you can make when choosing a build. Summoners dodged the big nerf hammer and only received some reductions to minion Life and Damage for Raise Zombie along with increasing the investment you have to make for your last Raise Spectre. Besides that, Summon Skeletons still wreck anything in their path and the best ascendancy choice is still Necromancer..
The Metamorph league mechanic is very non-melee friendly, but there are some skills like Cyclone that can still do a lot of work with a low budget. The classic Essence Drain/ Contagion combo still hits very hard, especially when utilized by the Trickster ascendancy.
Many people jumped on the Arc “hype train” and the skill became very good for clearing again after its chain range got bumped from 25 to 35 units. Arc can be self-casted, played as Totems, Traps and Mines or even used in Cast on Crit builds. It is pretty much everything you will ever want.
When it comes to Bows, which is the focus of this league, many of the basic Bow skills received significant buffs. Only Tornado Shot got nerfed and rightfully so, after being one of the best clearing skills for so long. Building an Ignite or Bleed Bow Attack build is something that would have been considered “hipster” in the past, but not anymore. It is now easily achievable because of new passive nodes on the tree and skills that provide great amount of Ignite Damage ( Burning Arrow and Explosive Arrow) and Physical Damage over Time ( Puncture). When it comes to other Bow skills it is now much easier to Freeze foes with Ice Shot or apply heavy Shock effects with Lightning Arrow.
This is just a small fraction of the most played builds in Metamorph 3.9 and there will be more to come in the near future.