well, acording to Wikipedia, Dimmu Borgir = Symphonic Black Metal. the synthysizer thing that i mentioned is the use of classical music elements in Symphonic death metal.
but as for their stuff, i've only listened to their old songs such as songs on Stormblast and Puritanical Euphoric Misanthropia. and just by listening to a few songs from those albums, i decided that i didn't like the band. i also saw a music video on Yahoo! Music which kinda sucked too.