Unconfirmed, but I heard it was a massive heart attack. Not surprised, considering how big he was and how he used to party.
Can't claim to have listened to all of Pantera but some of it like Cemetery Gates i enjoyed a lot.
The Great Southern Trendkill is my favorite album of theirs overall,
Cowboys From Hell is pretty good but there are some songs that I don't really care for one way or the other.
Far Beyond Driven and
Vulgar Display of Power are also quite good. I don't know shit about 80's Pantera and I didn't particularly like
Reinventing the Steel. Your mileage may vary.