I don't know whether to like this twist or not. On one hand it's the biggest twist since Dragon being Luffy's father, but what significance will it have to the story. Ace is already a very very wanted man, set to die… him being Gold Roger's son doesn't change a lot for him.
Now there's less of a chance that Dragon will come. So who will assist the Whitebeard Pirates because I can't see them winning as things go (I actually thought that a Marine Admiral was almost equal in power to Whitebeard). But I'm confident Ace will survive... I can't see Luffy letting anything else happen.
I've also been confused by Garp. He seems to be connected closely and positively to some really wanted people (Dragon and Roger) yet he's committed to the WG and just sits there and lets Ace be captured. Dunno if he's planning something or knows about something that is going to happen (maybe he has called Dragon who will appear after all)... but now we know that Garp took care of Ace for Roger, who's wish was for Ace to live happily (which lessens the possibility of him dying).