For those who are interested here is a comparison
Helmet - no noticed changes (Passive effect refills breath under water.)
Chest - damage reduction has been reduced from 100% (IC1) to 33% (IC2). Fire immunity is unchanged.
Legs - now are usable underwater (Active effect (hold L Ctrl by default) makes you run faster)
Boots - Fall damage distance has been shortened. Also are usable underwater (Active effect (hold L Ctrl by default) makes you jump higher).
Edit: Vid Proof
I am curious about this because Alblaka said on his blog that:
"Tier 3 armor will be highly advanced, even more overpowered then the NanoSuit and REEEEEEEEEEALLY expensive… as it is made of [iridium], which can only be created from UUM."
I find this annoying because without the invincibility I won't be able to go swimming in the Nether
Fortunately I have already finished my Nether tower... but still.
Edit: turns out its a bug. Yay!