My Arms, Your Hearse and Deliverance are the most straightforward metal albums they've done. Blackwater Park is a little more proggy than those two, but it has a lot of their best, heaviest riffs. Orchid and Morningrise are folky rather than proggy, and they aren't really heavy albums, but very good, with Morningrise being the better of the two. The vocal approach is different than on every album since, and the song structures are looser. You can skip everything else.