Okay, so the title's misleading. GW have done a brilliant job this time around.
*Jumps up and down with excitement*
Seriously, the BBB (Big Bloody Book) FAQ alone is more of a change than the transition from 3rd to 4th edition (or so it feels).
*Jumps up and down some more*
Of course, they'll never deal with the stuff I write about.
*Stops jumping. Just as well, really*
That's what I get for being a pedantic little bastard ('I'm not little!').
Anyhow, I guess you've already guessed that this won't be a deep analysis. No siree, this is a Caffeinated Squirrel (patent pending) post.
They've fixed stuff.
Units of characters (Paladins, Nobs, Wolf Guard) aren't anymore. No more LoS! shenanigans for you!
Weird power weapons across codices (Glaives Encarmine, Daemon Weapons, Logan's weird axe thing, and so on) have been fixed. They now have actual rules!
Flyers can no longer be hit by anything not firing Snap Shots (or cheating with Skyfire). The Death Ray is no longer the bane of fliers!
Look Out Sir! now relocates wounds to the closest model, not any model within 6". No more heroic leaps across five members of the squad to save Sarge!
The rules for charging for terrain now state that any unit from which a model has to move through terrain to reach the enemy by the shortest possible route are treated as charging through terrain. The rule works now!
Flying Monstrous Creatures can Skyfire. Also, Chaos Speace Marine Daemon Princes with Wings can now fly. No more looking on in envy!
The weird situations with Mixed Armour have been fixed. A character now automatically causes wounds to be allocated as for Mixed Armour, and Feel No Pain counts. Thank you!
Stuff that lower the Initiative of models in base contact now do so at the start of the phase. No more Piling in only to have your Initiative reduced, leading to massive confusion!
There's tons more, but those are the ones that jumped out at me.
*Doing the FAQ dance*