So a very popular strategy I've seen these last few games I've played in the beta, is to play as tyranids, and just fill up on ships that have a high amount of launch bays, rush towards the enemy, and take out the enemy in a single blow by blasting all your assault boats on a single ship.
I've no idea how to counter this, because all it basically requires, is for the tyranid ships to be close to your flagship or their preferred target for one tenths of a second before it gets instagibbed by the 10000 boarding actions it suffers. As if that wasn't enough, they can repeat these shenanigans once more a measly 60 seconds later.
The only way I see of beating this, is to fill your fleet with low cost vessels, which doesn't work either, because now you can't counter their tentacles (which are also superbly powerful)
I'm all for this game, but it feels very unfulfilling when battles are decided in 5 seconds when half your ships are reduced to drifting hulks because some nid sneezed at them.