It's basically Magic except that instead of having a limited set of cards with different known rarities, you have 104x10^24 decks and no one knows what the rarities of those decks are. Every time you drop 16 bucks on a deck, you might be buying the best deck in the entire world, or you might be buying an unusable dud.
Well, the first and most important difference is that you'll never have to face an unbeatable deck containing only ultra-rares. Similarly the algorithm that creates the decks will ensure you'll never end up with an unusable dud. Yes, you may end up with a deck that is slightly weaker or stronger than average, but overall the power level is about the same.
And because of the "chains", FFG has a plan B in case they overlooked something and a deck turns out to be stronger than it should be.
So, buying hundreds (or thousands) of decks in the hope of finding that needle in the haystack that is overpowered would be extremely stupid.
The only reason I'd buy several decks is to get an idea how the different factions work. And then maybe, once I've found out what my favorites are, try to get a deck that includes them.
For me personally, there's a third extremely important difference: I won't have to construct any decks. It's something I always hated doing. In games that require constructing decks, I always ended up net-decking. I want to actually play the game, not spend hours or days poring over hoe to create the most overpowered deck.
I have no idea yet how good KeyForge is suited for tournament play, but as a casual player, that's not something I care about.
