I'm looking at 3.0 for the first time in ages. It seems fine on the surface. What were the major problems that justified the release of 3.5?
I played core 3.0 without real problems. I also had the first wave of splatbooks, and still didn't have much issues beyond a few spells which required some adjudications to prevent abuse. I certainly didn't test all the material however.
When 3.5 came out I switched to it using the SRD (I was merely waiting before buying the books in order to avoid the usual errata phase). I played it maybe 9 months and gradually figured out it was worse than 3.0 because it was built with patches to perceived (for me, imaginary) mistakes, but without regard to how those patches interacted with each other. Instead 3.0 was at least designed "organically" and was more solid.
Generally speaking, you need to keep in mind that both 3.x versions were based on the idea of "system mastery", meaning that the game does have certain better options which players are supposed to discover while playing, and learning how to exploit them is a reward. However, it still does not mean the game should play itself like a videogame where the rules takes care of everything perfectly: the game still needs a human referee to work satisfactorily.
So why did they make 3.5? Many reasons:
- people insisted that the game needed to work like a videogame and saw flaws everywhere, and the designers were pressured to change things
- the internet era vastly amplified the perception of problems and the importance of being part of an "official" community: players were constantly reminded by others that the game they thought fine was instead unplayable, and lots of them would not stand the pressure of house ruling and demanded official changes
- designers ran out of ideas to keep up with the insane release schedule, and a reboot provided the opportunity to reprint slightly updated versions of a lot of character options
- key managerial staff at WotC had changed and new managers often need to push big changes to justify their jobs
If you want to try either 3.0 or 3.5, I think you should assume that either one will be OK, as long as you play your game without listening to doomsayers. And if you are undecided upon which, maybe take a look at what non-core material is available, particularly campaign settings books, and choose the one version that has settings you want to play most, so that you won't need to worry about converting minutia.