Interesting battle Hena. In my last few games we've had a number of occassions where assaults ended up going contrary to "the odds" such as occured in your game here. I guess it's the "random factor of war" (which is why I think it works more for Orks than anyone else

).
I have to admit I am not up to date with the Tyranid rules, but your game
looked fairly balanced (well it looked like a bloody slaughter, but a balanced one!).
Looked like the Marines were suffering from a fair amount of attrition though. Do you think the Tyranids would have turned it around had there been a 4th turn (assuming you made your rally)?