What subgenre of metal is "To Mega Therion" by Celtic Frost?

[Texas King]

In your opinion what is a primary subgenre of metal for this album?

This album is considered a significant influence on black and death metal and it's even labeled as black metal by some Internet pages but to me it doesn't sound like black metal musically or vocally.
I'd say it's a hybrid metal album, primarily thrash metal with some doom and heavy metal stuff.

What would you say?

 

[no country for old wainds]

if i was going to pick one it'd be thrash or first wave BM, but every single genre you mentioned is applicable to some extent. it's one of those rare albums that's near impossible to pigeonhole.