After killing all 6 of them there's not much to say... Unmemorable. They all are twitching and die pretty fast.
Azys Lla is T10 cat boss without reskin or recolor, dies in 30 seconds without really hurting anyone.
Forelands has a giant blueish griffin, very safe hunt which doesn't hurt. Dies in 20 seconds.
Hinderlands is a recolored blue headless rider aka the first boss of AK HM. Basically it's Agrippa part 2, at some point it reflects all damage and you'll see a lot of bodies of bad players. But, because there's no any new mechanics, it's pretty disappointing. Can take up to 90 seconds to kill.
Sea of Clouds has a medium sized bird, I think its T12 boss? Not sure, because it died in 20 seconds.
Coerthas has the same Behemoth from old Coerthas FATE and LotA, but it can use Meteor 2-3 times before diying which can kill some nearby players. Nothing new really.
Mists has an unmemorable boss which looks like one of 2 final bosses of Stone Vigil HM. But because it has such low HP as all new S ranks it melts pretty fasts so you'll not even notice his attacks.