One issue I've had, and that I've heard repeated from many "old school" magic players, is about how the "new sets are overpowered". It's true, there's tons of ridiculous one-shot win the game (or never lose the game) types of cards out there. Or absurdly cheap cards from a mana -> ability standpoint.
Of course, if you go dig through the old sets, there's a ton of crazy things that have always been around. And from what I hear, the playtesting wasn't nearly as rigorous back then either, which resulted in many more "broken" combos/etc. So maybe there isn't much difference after all, other then finding excuses not to blow more money on silly cards.
But the conclusion I came to was that Wizards was aiming for everyone to have that "killer deck". My unbeatable deck versus your unbeatable deck means two players sit down both thinking they're awesome, and then have a brutal game where no punches are pulled. It works remarkably well. At this point, we have a stable of about 8 terribly evil decks that are all geared to win in 5 turns or less, and playing them against each other is some of the most fun I've ever had with Magic.
On the other hand, I hear the next core set is coming out this week and I really don't need to be buying another display box of cards. But I will. Oh yes I will.