I'd recommend their debut album, Penetralia. Its straight up fast brutal death metal, but it has some of the best riffs I've heard for that genre.
Osculum Obscenum was the same type of stuff, but less fun.
Then they slowed all the music down and it just became boring in the later albums, till they finally got back on track with Virus. Virus kept the melodic elements of the post-osculum albums but added the speed back.
I'd recommend getting Penetralia and Virus for the best of both worlds.