A somewhat lesser known band from the time when Pantera sprouted. They were even colleagues of sorts. Anyway, Pantera continued on working and building the fame they enjoy today (kinda), while Exhorder disbanded after two albums. Great albums, I might add.
Since they created music at the same time, they were influential to one another, so you'll find some striking similarities. It is, of course, thrash metal with a lot of groove goodness within. The vocals are basically the same and Exhorder's Kyle Thomas has obviously greatly influenced Phil Anselmo.
As far as the albums go, in my opinion The Law beats Slaughter in the Vatican to a pulp. However, they're both excellent. I'm sharing both, so you can be the judge.