Hmmm... being as I've got some rare free time, I decided to download several selections from each of the bands you mentioned. Decrepit Birth is actually pretty good, some really good musicianship there, but all the endless blast beats really start to sound the same to me after a while, to the point of extreme monotony. Same with the vocals. Of course, that's one of the main reasons I prefer Opeth, I like a break from the non-stop Cookie Monster once in a while! That said, they can definitely play, and if you're looking for all-br00talz-all-the-time death metal, they're a pretty damned solid choice.
I've got ObZen, and there's pretty much no break from the screaming there, either, although they do mix up their beats and come up with some monster grooves at times. These guys may be one of the most technically gifted bands on the planet, their level of musicianship is
insane, but I've got to be in an especially pissed off mood to be able to listen to them for very long.
I actually really dig Gojira, though. They do mix it up some at least, and for some reason, I just find them much more interesting and listenable for long periods of time than any of your other nominees.
Origin... wow, I'm picking up on a pattern here... all blast beats, all the time. Again, excellent musicianship, difficult to tell one song from the next.
Don't get me wrong, I like a good blast beat every once in a while, and I don't mind good death metal vocals, either, I just need more diversity in my music, although I completely understand that there are a large number of people such as yourself who just dig 24-7 br00tz. Nothing wrong with that, and to each his own, but I wouldn't say that Opeth is "overrated" compared to these bands, they're just
different. I'd even go as far as to say it's really not even a legitimate comparison. Bloodbath would be much closer to that vein than Opeth is. Opeth has really never been an exclusively death metal band, and has always displayed a much wider sphere of influences than the other bands you mentioned, with far more prog, folk and straight-ahead metal flavors than any of them. Again, not that this necessarily makes them better (that's entirely subjective), just different. You dig the br00tz, nothing wrong with that, just understand that some people like a tad more diversity in their metal.
Thanks for the entertaining listening suggestions and much-needed diversion, though!