The main problem with TCGs is overcomplication. They start out fine, but each new set adds new rules and cards (in order to increase incentive to keep spending money), which only wind up ruining balance and destroying the learning curve.

Try stepping into YuGiOh now. You will be utterly lost amid the hundreds of variations on the rules that came out since the original game. Some of the others have faired better, but there is a reason why Magic: The Gathering keeps releasing "intro" sets like the Portal expansion.

Oh, and I've only played the Pokemon TCG on the GameBoy, but it was the most laughably broken TCG I've ever played. As soon as you understand the rules, you could exploit the heck out of them and almost never lose.