I do not go around sniffing for exploits but oh man those things made me facepalm lately ... it's the most exploitable mmorpg i've played.
Here some ...
-exploitable delve boss farming (reported in beta fixed just recently)
-hireling exploit (not the dupe, the 7x4 hirelings thing)
-Explotiable dungeons - many bosss mechanics can be denied by pulling boss away from it's spot , some skills bug out bosses making them tank and spank, not to mention the infinite loot exploit.
-PvP exploits - from Bolt scoll runnes, speed stacking to batsofdoom
-exploitable grind spots - fast infinite respawns
-motif farming via relog (nerfed a bit lately)
-animation canceling
They need to get their $#!7 togather and dare i say it PROPERLY TEST upcoming content ?