You are able to describe the rules so quickly only because many of the concepts are already known to most humans. In the case of aliens, you can't expect them to use a language in which words like "entity" or "adjacent intersection" are defined like they are in English. Most humans understand those things without further explanation, but if you tried to define the rules mathematically with perfect precision, you'd find the difference to Chess to be much smaller. A rough approximation would be programming a simple interface that allows you to play Go or Chess (such that the interface can keep track of "chains", detect captures, count the score and whatever else is needed), while a better approximation is making such an interface without relying on anything human-made (like an existing programming language).

What makes Go appealing to us humans is exactly this difference: In Chess, the rules are not intuitive, so explaining them wouldn't be easier than programming them. With Go on the other hand, we have intuitive notions which help us. The same can probably be said for the playing strategy, but you've probably heard that before - "Go is strategy and Chess is tactics", or something like that. You can't expect aliens to have an intuition similar to ours, so they might not find the rules simple or the strategy deep.

I'm probably making wild unsupported claims here, but I like using programs and computers as an example of an intelligence that doesn't resemble a human one. Also, chess is probably a bad example as it is also human-made, so there might be games that appear even more "baroque" to us, yet simple to aliens.

If the aliens are intelligent and scientifically sophisticated, they'll understand axes in a two-dimensional space. It would be pretty surprising if they didn't know about perpendicular axes.

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Occupy Babel!

Actually, the reason I can describe the rules so easily is because I recently programmed a go interface. Defining `entity', `intersection', and `adjacent' is a trivial matter; `entity' has already been defined by the English language, and any other language is likely to have a similar concept because it is universal. Meanwhile, the other two words make perfect sense as soon as you make a goban (shape and dimensions don't particularly matter). They will indeed be different for different kinds of boards, but this changes strategy, not mechanics.

I haven't programmed a chess interface yet, but I can say with a good deal of certainty that programming rules for chess would be far harder, and the difference even greater (that the pieces would be implemented differently is obvious; but I would design the board in a completely different manner, too, with far more bookkeeping to be done).

As for games that appear baroque to us and simple to aliens: I wouldn't be surprised if there was a race out there that intuitively `got' the Game of Life. It's another one of those things that we can be fairly sure aliens would have come across, again due to its beauty and simplicity.