[johnloeber]

The game depth for those games is going to be enormously large. Chess is played with 32 figures on a 64-tile board, and that's enough to give us serious problems. Games like SC or LoL have way, way more options -- the set of all possible game states is of such a size that I don't even have a sense of scale for this order of magnitude.

Think about it this way: the average branching factor of a legal chess move is 35: there are about 35 legal moves that could follow. For Go, the average branching factor is 250. In StarCraft, how many "legal moves" do you have available at a given game state, on average? Tens of thousands? Millions?

By the way, this is made significantly more difficult by SC and LoL not being turn-based games the way Chess is.

[lmm]

Maybe. There are indeed many possible moves, but how many represent important strategic choices that take learning to understand, and how many are just the obvious thing that even beginners will see how to do after a little study? (there are plenty of "broken" RTS games where there are millions of choices but there's a clear winning strategy in building lots of one particular unit as fast as possible - StarCraft is the exception and not the rule in sustaining interesting gameplay years after its release).

And if we're talking about computer playability, the real-time nature of these games cuts both ways; in StarCraft analysis we literally talk about how many "actions per second" a player was able to execute, a field where a computer will naturally have an enormous advantage (part of why I prefer to play Supreme Commander).