If you played starcraft 2, well no need to read this review-simply buy this expansion
if you're a newcomer, stay a while and listen:
starcraft is a real time stratagy with 3 different factions who play completely different from one another
you have the terrans-the humans who use technology
you have the Protoss-the cool looking aliens with Psi blades/warp blades and "space magic"
and the zerg, the flood like alien beings who consume all in their path
if you haven't played starcraft 1 don't worry, there is a starcraft 2 Mod called starcraft recall and it will get you understanding all previous story, but if you don't have the time to play (or watch) the overall events video sums up things pretty nicely and playing just wings of liberty and heart of the swarm is enough
any case, multiplayer: don't play until you've mastered the campaign but i do recommend you guys to play archon mode which is Co-op red alert 3 style
as for the campaign you'll get hooked up just like warcraft 3 back at the day
you can get starcraft wings of liberty (the base game) for like 10$ on G2A (same goes for heart of the swarm expansion)
so a measly 40$ for legacy of the void pretty much sums up 60$ for a really HUGE RTS with great story (esp the protoss campaign)
and i do recommend to everyone who played warcraft, hell, even halo wars to try this amazing franchise.