Therion and Rhapsody =Prog; Death is not?

I don't think that Death are progressive at all - they try to be technical, but there's nothing progressive about the music (I was in a band playing in a similar style nearly 20 years ago).

I don't know the other two bands you mention - but judging from the mp3s on this site, Therion are a pretty vanilla Heavy metal band, with immaculate production, a good taste in Gothic choir sounds and half an eye on the progressive market. The riffing is bog standard metal though. YOu might as well compare them with the Moody Blues "Days of Future Passed"; a bunch of good songs with professional musicians brought in to pep it up a bit. Don't get me wrong - I like it!

Listening to the Rhapsody mp3s, "The Bloody Rage of the Titans" has a nice arrangement, with basic synth/orchestral parts but again is pretty much standard metal and reminds me very much of early Helloween. I find the choir less effective than on the Therion track, and the recorder playing above the power riffs is just silly - reminds me of Spinal Tap's "Stonehenge".

"Symphony of Enchanted Lands" has some great atmospherics and there's that recorder and quasi-Mediaeval sound - but it's all basic stuff. It may be a kind of progressive approach, but it's not really on the same level as "real" prog - prog related, maybe.

As for Death, "Scream Bloody Gore" and "Leprosy" are not prog any more than Slayer are, but pure (fantastic) Death Metal - that's the point of both albums. "Sound of Perseverence" is that kind of "technical" stuff that metal bands seem to play when they want to be known as prog - and it doesn't work as prog, IMO.

But YMMV