I've played 20 hours, got 80% of the achievements including winning once with each faction, though I've been playing on easy.
I played on normal all the time, got all the squad-specific achievements except the one that asks to complete the first 2 islands in less than 30 minutes with the Blitzkrieg squad (come on, I like turn-based games for a reason, you can't force me to rush!), I wonder if I could do it on easy. Did you complete that one?
I saw a YouTuber play on hard, and the worst thing is the final mission, where you get
all alpha Vek, so you can't get one-shot kills and you need to be able to always move them. I'll try to play hard once in order to unlock the achievement for completing 1 hard run, but I have to choose a squad that excels at moving Vek.
Basically, this game doesn't have the moment where you go from just drafting the most powerful cards you see to drafting around a strategy.
Well, maybe I pushed the "card game lovers will like this" thought too much, but I didn't mean to say that it's just like a card game, of course it's not. Based on my experience, since I liked this game because of the strategy element, there will probably be other people here who will get hooked by it, that's all I meant.
You can actually find some synergies, not between mechs, but rather between pilots and weapons.
Silica, for example, is the pilot I have always brought back after each run because his special perk is the one that allows for more "broken plays" with the right weapons: you can act twice if you don't move. Give him a weapon that makes the mech move, and you can move him twice along straight lines while doing stuff. Or put him in the mech with the Cryo Launcher (it freezes both yourself and the target), and you can shoot ice and then repair in order to free yourself from the ice.
In my Rusted Hulks run I have been so lucky to find the weapon that generates smoke on the mech's tile and in the 4 adjacent tiles, together with the pilot that is unaffected by smoke and webbing (usually, anything coated in smoke can only move). Rusted Hulks are already smoke-based (they start with a passive that makes smoke deal damage to enemies) so the synergy was great.