It's still D20 anyway you slice it.
They're not changing anything horribly fundamental, like what Attribute bonuses do, saving throws, hit points... skill checks still work the same, weapons and damage are remaining the same, most feats aren't changing...
So a few spells work a little differently, and some class' spell lists are changing. So far of all the scanned images, I really liked everything I saw.
I wish they had explained Attacks of Opportunity that nicely when 3.0 first came out!