I think the only thing I "hate" about 3.x is that it requires a lot of prep time, and that it demands a lot of attention on the part of the DM to oversee what players want to bring to the table, character options wise. One powergamer with one late 3.5 supplement can ruin an entire campaign.
You had to bring the "H" word into it.

When I DM, prepping NPCs can take time, but I rather enjoy making characters, tweaking them to fit exactly the personality and position for the game. And the 3.0 DMG was awesome for prepping NPCs or even winging them on the fly.