In which context do you mean limited release?

The first wave has a limited number of prints, but Unbound will be in print until the next booster set comes out.

so out of all the cards, which do you think is the most powerful card.

I looked through the gallery and there seems to be a good balance of cards. Without knowing what all the abilities are on them I am not too sure what can be determined as powerful just yet.

The stuff with Area is going to be difficult to over come. Given the Falling Stones #156 with Area 4 boosting it with a Kobold would be very intimidating.

I read on TCG player that Greenknee has some very interesting abilities. I am curious to see how that is going to work out.

There are some scary dungeon cards that when they hit the table have to be dealt with either right away or before they "go off". Area effects can be nasty, and so can poison. Falling stones and lava pit have nasty multiple target attacks.

For crawler cards there are hands down those useful cards that you need in hand at the right time like Primal Environment or Moving Search, but pretty much all are useful in the right situation or really versatile like Teamwork. Believe it or not one of the most useful I find is Wooden Shield and I love Brawling to soak up some damage.

To deal some great damage fireball and cleave can really clear out an encounter nicely.

Hide and Shield Ally can really mess up your opponent's plans in competitive formats.