Specializations are new for me. I have a typical SMG character, with Commando, Spec Ops, Three-Pointer, Grenadier, Ballistics, Suppression, etc...
Given the situation of large crowds and tough enemies in Expedition, I am thinking the suppression specs might be useful. Ranged-combat suppression looks handy for certain enemy crowds, and I like the AP reduction specialization, as well.
The problem is that there are four or five sub-branches of suppression specialization, so I am not sure what to invest in. But I like AP reduction and range-suppression.
Then there's the grenades. One of the specializations will allow me to reduce the cooldown time of grenades, which is pretty significant.
I also like the 3 AP increase for each kill that comes from Commando or Spec Ops (I forget which). That's a definite one for me.
There's the one for Ballistics, that enables you to increase the DT of the vest by 1 for each level (up to 3, I think). That seems cool, if I'm making more vests. But am I? I have endgame vest equipment already.
Then there's ones that seem potentially useless. I have Escape Artist, but only to get out of traps. I don't need the extra AP after escaping that the specializations provide.
I think the specializations for the meat-and-potatoes feats of the build are best, such as Commando / Spec Ops, Grenade Cooldown, etc...
Are the specializations that increase grenade damage worth it? By the time you're in Expedition, grenades only kill enemies that are already easy-to-kill. What about the damage boosts to Expertise that specializations provide? Are they worth it in late-game?
The only ones I'm sure about are the extra 3 AP per kill, maybe the bonuses to suppressive fire, and maybe the grenade cooldown reduction.