Ther are no "must have" skills, since you can finish the game with crap builds too.
But here are some of the most usefull skills anyway (just be aware that they might get nerfed in the release version):
- Adrenaline
- Teleport
- Skin graft (skin graft + adrenaline is incredible powerful)
- Clear-minded
- Haste
- in general self teleporting skills are very usefull (Pheonix Dive, Tactical retreat, etc.)
- Spread wings (extremly useful to walk around the battlefield really fast)
