delericho
Legend
A lot of it is emergent issues: the problems were there all along, but they weren't noticed right away. And they tended to be noticed at the same time as supplements were introduced - often, as those same supplements made the issues worse.
It's also true that the biggest issues in the core were things that you could very well miss entirely: if your group tended to avoid multiclassing, if you played at the low-mid levels (up to the teens), and if most magic items in your campaign were found (rather than bought or crafted), you might very well not hit the biggest issues.
(Oh, I suppose you should add "and they avoided polymorph" to that list.)
There was also a big question of how much you really cared about the issues. There's a really old "Design & Development" column that talks about "proud nails" - things in the game that aren't quite right, but that aren't game-destroying. If you let such things get to you, though, they can quickly suck the enjoyment from the game. 3.5e, including the core, had a lot of proud nails... but if such things don't really bother you, it's not really a problem.
It's also true that the biggest issues in the core were things that you could very well miss entirely: if your group tended to avoid multiclassing, if you played at the low-mid levels (up to the teens), and if most magic items in your campaign were found (rather than bought or crafted), you might very well not hit the biggest issues.
(Oh, I suppose you should add "and they avoided polymorph" to that list.)
There was also a big question of how much you really cared about the issues. There's a really old "Design & Development" column that talks about "proud nails" - things in the game that aren't quite right, but that aren't game-destroying. If you let such things get to you, though, they can quickly suck the enjoyment from the game. 3.5e, including the core, had a lot of proud nails... but if such things don't really bother you, it's not really a problem.