Thanks to a helpful commenter at Wowhead, I have the following comparison between this set and the Season 1 equivalent, Gladiator's Battlegear. The new set has, as compared to the old one:
+22 crit rating
+18 hit rating
The gem slots and set bonuses remain the same. It would be nice if you could mix and match between Season 1 and Season 2 sets in order to get set bonuses, but I'm not sure whether this is actually the case.
Hopefully stats on the other sets will come to light soon; if that happens, I'll update this post.
Update: skins and set bonuses for all the classes' sets are now available.