I just think Civ--all versions--is a challenging game because of its complexity. As a result, you can have good games and bad games at the same level. When it happens to me, it's usually because of a lack of concentration.
Case in point: my best games thus far have been the ALC games, which I post here on the board. To a great extent that's because of the advice provided by those who respond to the threads, but to some extent it's because I just stop playing and take a break between each set of turns. My best games for which I don't get group-mind advice are, again, those I play slowly, with frequent breaks.
I say this because of the well-known enthralling nature of the game, that "just one more turn" appeal it has. But guess what, at 2 AM, after playing for six hours straight, you just might not be in the best frame of mind to keep up with the AI! Same problem after a tough day at work. At least that's been my experience.
I can't speak to playing at the higher levels, since I'm a Prince-level player myself (though I did manage to beat Monarch just recently, after 12 attempts). It sounds like Naokaukodem's frustration is that the same strategies that work on the lower levels don't work at the higher ones, even if you try to adjust them accordingly. Instead, you have to rely on tactics that some people consider "tricks", like chop- and pop-rushing, slingshots, and so on. I've noticed several posters who feel that these sorts of tactics are dishonourable or dishonest in some way.
I can sort of understand that. To a large extent, these tactics are needed because the AI at the higher levels has an "unfair" advantage and you need to claw your way back somehow in order to compete. Saying the AI is not smart enough is a legitimate beef about the game, but programming an AI is difficult--which is to say, time- and resource-intensive and therefore expensive. We've probably been given the best AI that Firaxis et al could afford to give us. Could they give us a better one if they accepted less profit (assuming they are making a profit)? Maybe. How much better, though? There's such a thing as the law of diminishing returns, after all. And the simple reality is that Firaxis is a business and their main goal is to make some money off of this. No profit, no expansion packs, no next version.
Beyond that, my own feeling is that these tactics are part of the game, and none of them, in and of themselves, guarantee success. They can certainly help, but in my experience thus far the same basic strategies have taken me through to all the levels: specialize your cities, pay attention to your military and power ratings, balance your research, maintain your diplomatic relations.
I enjoy playing the game and still find it challenging, engrossing, and most of all, FUN--even after several months of ownership and many hours of gameplay. It was well worth the 60-some-odd canuck bucks I paid for it. Could it be better? Of course. But it's pretty darn good just the way it is and I like it just fine.