Omnotron is more boring than hard. It's a dumb nuke, but you have to start with Magmatron, because he got a lot of long-casting specials during when he does not melee you. All other three bosses will destroy you and if you can survive, the second spawn will kill you outright.
Go with a full DPS build, blow everything and kite :)
Armory : eu.battle.net/wow/en/character/hyjal/Araitik/advanced
Music from NoCopyrightSounds : OLWIK - This Life (feat. Johnning) [NCS Release]