Haven't heard obsidian conspiracy, but i've got most of Nevermores' discography at home and i like Warrels vocals a lot. It's what made them stand out. Sure he's not brilliant all the time, but most of the songs are great (i think the disharmony was the selling point of Nevermore, if we don't count Loomis' solos :D ).
I think Loomis and Williams will just continue doing more of the same (if you listen to Loomis' solo record, it's pretty much Nevermore with solos instead of vocals). Warrels album is a bit more out there, but still similar-ish enough thematically (though i LOVE his cover of Lucretia my reflection)
I just hope they don't fall into generic-ness and start sounding as every other powery-thrashy-melodicy-band out there, cos i'm really fed up with symphony x, evergrey, scar symmetry and similar sounding bands at the moment