From: London, U.K.
I find that the AI is a reasonable opponent in games where I assault as the human player.
Even then, it almost always mis-times and mis-handles counter-attacks.
Its behavior in games where it is trying to delay me or in meeting engagements can be questionable, but in attack it is simply inept.
There are so many artificial ways in which you can get it to do what you want and then rip it to pieces, it is no fun.
If you want to defend and you want a challenging game, you must play another human.
I have only ever played against the AI, because of time constraints (I never know how much time I can give the game over several days, and games that take longer than a couple of days to complete can't hold my interest). When I want to make things more interesting, I play hotseat against myself.
This takes longer, but can be more exciting if you can be impartial about who wins or loses the game.
You sometimes have to say "if I did not know that his infantry is waiting in that clump of bushes, I would send my recon/tank/squad in, so I will..."; if you are uncertain you can toss a coin and leave it to fate.
This approach is not so much about competing, as about observing what could have happened.
It is not perfect, and I would love to play against a human player if I could find someone who lives around the corner so that we could play hotseat and finish the games quickly.