All the good bands on Sumerian:
After the Burial
Born of Osiris
Conducting from the Grave
Veil of Maya
(I haven't heard Dead Letter Circus so I can't comment on them). Unfortunately all of those bands minus Conducting from the Grave (and T.R.A.M who wouldn't fit on the bill) are on another summer tour so Mayhem Fest was left with a majority of the mediocre and bad bands on Sumerian.