I've played both a little 3.5 and played and DMed 4th edition. Unfortunately, I had a bad experience with 3.5 (I was a new player and our DM blasted through all the game rules and didn't allow us to ask questions or explain anything to us), but I'd love to be able to go back and play 3.5 with a different DM and see if it's any better. 4th edition is nice, but it's a lot simpler. There aren't very many skills and it's easy to deal with having a dump stat (INT or CHA or STR are usually good stats to dump, depending on race and class). Intelligence doesn't matter as much because the number of skills is dependent on your class (and race). Wisdom is only really useful for perception/insight/heal (or if you're a divine class). Dexterity is not as useful, as intelligence can be added to reflex and armor. Even with the simplification, you can always use "old rules". In the campaign I ran, I told people that if they wanted to specify their character's alignment (as per 3.5), then that would be cool with me. So there's a bit of houseruling that you can do to make it a little more like 3.5 in some ways (personally, I like the option of letting a character be "chaotic good" or "lawful neutral").