it could have been so much better. (spoilers)
it advertised differant campaigns for each race. thats only like 20% true. basically, its the same campaign with different dialogue, some new units, and enemies being switched around in some missions.
the biggest difference in story between the races are their reasons for fighting Azariah Kyras at the end.
Space marines: retribution, purge their chapter of corruption.
Orks: stop kyras, otherwise they cant loot anything.
Eldar: they have a craftworld hidden beneath the surface of typhon (or one of the planets) and the inquisition could badly damage/ destroy it.
Impearial Gaurd: aiding the inquisitor so as to stop the ordo malleus from destroying sub sector Aurelia.
Tyranids: the new tryanid swarm is under threat by kyras and needs to stop him so they can continue living and eating.
Chaos: (to be honest, when i played chaos i thought i would get to be the guys causing all this destuction, but no.) your leader wants to stop kyras, because Kyras is out shining him in the eyes of the dark gods.
so yeah, exactly the same missions, differant dialogue.
actually, thats pretty much the only thing that bothers me about this game. i mean, its story in general is....ok, but just playing it again and again but with different units is......boring (too me) i just use the same tactics again and again. (tip: a full imperial guard army of just the bsaic footmen can, with sustained fire, kill most things pretty quickly)
on the multiplayer side, even though i'm terrible at PvP, the new units to bring up the enjoyment levels. that, along with a few new maps does make it worth checking out. (sadly i have no idea how the army level/ experience thing works).
and as for The Last Stand (ultimately my most favourite part): the new achievement based items are pretty cool, and the imperial guard lord and his sniper rifle are a great addition.
(tip: when on last stand with the lord general, the sniper rifle really is one of the best weapons he can use. couple it with any equipment that increase either your stamina amount or recharge rate, then use the ability for a really powerful sniper shot to pick off the larger enemy and you can be unstoppable)