Unitron
Even though considered part of their "glam era", Power Metal provides some of the blueprint for the masterpiece that is Cowboys From Hell. Judas Priest meets Kill 'em All-era Metallica for an album that sounds like an early thrash album, and if it was released in 1983 or 1984 instead of 1988 I bet it would've been looked at in a better light.
I really like the band's first three albums as well, but everything is definitely turned up to eleven on this album. Phil Anselmo has more edge and bite than Terry Glaze, and was needed for the increasingly faster and aggressive direction they were heading in. His vocals are mostly in Rob Halford-esque screaming rather than the gruffness found on future albums, and it fits perfectly for the early thrash sound. There's so much energy on this album that it's impossible for me to not get instantly hooked.
Over and Out is a favorite, and includes a similar breakdown to the one found in Domination off of Cowboys. Straight from the start, Dimebag's always had a signature sound with both the riffs he wrote and especially the soloing. The whole album's great, but the breakneck speed of Power Metal, and pure thrashers Down Below and Death Trap are also among my favorites. Another is P*S*T*88, the only song in Pantera's discography with Dimebag on vocals, and he sounds a lot like James Hetfield.
The next two albums are my favorites from the band and two of my all time favorites, but Power Metal is not far behind.