As BC-A pointed out, Mabool is indeed the most easily accessible of Orphaned Land's releases but the truth is, whichever album you listen to first, you'll get the others sooner or later anyway and will end up loving each and every one of them. My personal introduction was Mabool, but depending on my mood, I prefer their earlier stuff. As for Kobi's vocals, they're more death metal style on El Norra Alila and Sahara. What other bands do you listen to? Maybe that'll help you with your decision.