After scanning through the errata, the only change to my game is a couple of spells (e.g.
phantasmal killer) make saves at end of turn, instead of start of turn.
That's it. Everything else (in my game) was basically just clarification of things we kind of knew anyway. A monk's fists aren't valid targets for
magic weapon. You can't Twin Spell a
burning hands or a
scorching ray. Reach can be used for opportunity attacks. You need a hand free to load a missile weapon (i.e. the bolts or bullets don't somehow jump into it automatically). In all honesty, my players would have been surprised if anyone at our table had a different interpretation to this, or if our DM would somehow allow it.
Of course, other people's mileage my vary. If anyone out there disagrees with a ruling, the good news is that it can be ignored. Their DM decides the interpretation anyway, so it only impacts organized play. And if my participation in organized play was contingent on whether my sorcerer can Twin multi-target or area-effect spells, then... well, even without the clarification, I'm probably asking for trouble with the DM.
I'm pretty happy about it, overall. I generally hate and fear errata, because I feel compelled to place stickies in my books or have print-out sheets lying around. But there are no really significant changes here. Frankly, I could ignore this errata completely (other than a mental note that a few of the ultra-weak illusion spells are now ever-so-slightly better), and it makes no impact to our game. Excellent news.