Seen this quite a few times already so here's my opinion.
Standard flop call. he has the nut flush draw (9 outs) the nut gutshot straight draw (4 outs) and possibly the A will be good sometimes here too possibly adding another (3 outs). With so many outs i'd rather get it in as soon as possible personally to avoid very difficult spots like it became on the river.
The flop call is alright too although i'd prefer reraising personally. I'd only see a reason to just call is too make Tom keep bluffing and get the most chips out of him. That's what i think Ivey was doing. THere's so many draws out there it's not that unlikely Tom Dwan is drawing. He could also obviously have a very strong made hand already. So Ivey calls a 3/4 potsize bet on the turn. He's not calling for odds anymore. So he either thinks Tom Dwan is bluffing, weak enough that he can bluff him out of the hand on the river if he misses or can get paid off enough if he hits on the river to make it worth to call. I personally don't think he's going to get paid off when the flush or straight or A hits so that makes the last scenario unlikely. I don't think Tom Dwan could continue with his bluff if any scare card hit on the river like A, J, 9 any diamond and probably T,Q,K too. So in my opinion after making that turn call your not ever folding blank rivers. Either raise or call.
Seeing as he thought that long about calling the river i'm pretty sure Ivey thought he was bluffing. But because it was so much money and such a sick bluff by Tom Dwan that he started doubting his own read. He had the right read but didn't have the balls to put the chips in.
Exept for hitting his outs those turn and river cards are the best Ivey could hope for. Complete blank on the turn and atleast makes a small pair on the river. Which probably doesn't change much most of the time but it's atleast something. All draws miss too.
I'm not sure if i like Tom Dwan's bluff that much. But he does have the heart to pull it through and not give up on his read like Ivey did. The turn and river were also the best cards he could have hoped for since all draws missed and ivey was drawing. Perhaps he was going to represent one of the strong draws when they were hit then he wouldn't have liked it. But if he could have seen the hole cards he'd realise how lucky he got with the turn/river.
To sum it up. Vs a player like Tom Dwan and those blank turn/river cards you could definetly justify a call by Ivey on the river. It's a very hard call but possible nonetheless. I'm not really sure what Tom Dwan was thinking to be honest or what his read was. But he got the best turn/river cards he could hope for if his read was that Ivey was weak or drawing.