Love: Many things, most of all how easy it is to DM. I really enjoyed my Epic 4e campaign, and I will never have the fortitude to do one in 3.5.
Hate: It's a bit weak to be a "hate," more of a regret, but I miss all the weird, cool spells. As a spellcaster, I really felt powerful in 3.5. (Playing a druid frequently probably had something to do with it, too!) But there really isn't room anymore for stuff like oldstyle Ray of Enfeeblement or a permanent Baleful Polymorph. (To say nothing of turning into Shadow Dragons!) The biggest injustice is what was done to poor Forcecage, I wish it had become a ritual or something.
Taking down a Great Wyrm Red Dragon in one turn with Assay Spell Res, Imbue Familiar and a few metamagicked-to-hell-and-back Enervations was a thing of beauty.
Now, I fully realize that the stripping of these things was in part what made DMing so much easier (and the game so much more balanced), and that's why it's more of a regret. But that doesn't mean I won't be a little bitter.
The only thing I really hate is the lack of PHB shapeshifters. But I expect that itch to be scratched by March.