It's currently simply about collecting cards, as you can get them in card packs, but you can also trade them with others on the market.

In september, Tournaments will be released, which will allow us to fight with the Steem Monsters, but it's likely that the card values will increase as we come closer to the start of september, so everyone is collecting actively already ;)

I guess there's a certain amount of hype around it for now. Stats of the steemmonsters are also being released very soon, according to the steemmonster folks.