Honestly I completely forgot about the whole game coming out.
How long was the campaign in hours played, and how would you rate it?
I played about 70 hours, it's probably doable in less (I heard something around the 50 hour mark somewhere).
The campaign doesn't force any time limits on you, so it can be a good idea to take regular mercenary contracts to shoot yourself some better mechs and gear, train your pilots, and upgrade your ship for better repair facilities, medical facilities and morale-boosting amenities.
how much is it like the FASA board game?
It is different, but still with many similarities.
You still have to do heat management, you have all the different hit locations with their seperate armor and structure values, with the chance of critical hits.
Positioning matters, if you shoot from the side, you have a higher chance of hitting locations on that side, if you attack the rear, you get to attack the soft rear torso armor and stuff like that. If your morale is high or a mech has been knocked down from stability damage (ballistics, missiles and melee inflicts stability damage in addition to regular damage) or having lost a leg, you can also take called shots to specific locations, but normally it's random.
Initiative is very different. There are 5 phases, one for each weight class and an additional one for particulary trained pilots in light mechs. The lighter the class, the earlier its phase. In your phase, you can choose to reserve to a later phase, or act, allowing you to move and then fire or use some special options. Within a phase, the sides switch. (So lights for example can reserve to the end, move, take a shot, and then the turn is over and the new phase begins, and they can sprint away again before any heavier mechs can act to their presence. Particularly trained pilots could potentially also attack and then move.)
Mechs come with stock loadouts, though you can tweak mechs in the mech lab. You can't change the engine, and mechs have hard points that limit where and what kind of weapons you can load. (So you can't turn a Hunchback 4G into a missile or laser boat).
There is also the metagame of managing your mercenary company, you take contracts that hopefully earn you money and salvage. But you have to repair any damage your mechs took (potentially replacing destroyed mech parts), and your mechwarriors need to recover from injuries taken in the fight, or need to be replaced because they died from those injuries.