Great stuff.
Not all Prog Metal outfits are quite so vocal-forward. For many, the singers are talents beyond belief who are competing for air with mind-boggling talents on the guitars, keys, drums, and bass, while performing Super Mario-esque jumps to manage the tricky timings. The voice ends up being just a requirement, or in some cases, a bug. For Sullen, the lead vox are a feature.

David Pais issues a variety of vocal attacks - - harmonies, clean, growls - - channeling such varied parallels/influences as God Lives Underwater, Between the Buried and Me, Into Another, Stabbing Westward, Aeon Zen, Opeth, In Flames, Fear Factory, Tool, Alice in Chains, and - - you get the point.
Sullen do employ the other usual suspects of Prog elements: smart-deep conceptually-linked lyrics, fascinating time signatures, sweep picking. They come across as nerdy, focused, serious guys who are usually the smartest in the room. That’s not meant as a cut; it’s a good thing.
I’ve listened a number of times now, and I still feel like there are little secrets to discover, hidden passageways and hidden artifacts in the songs. The density is not cloying and frustrating, these songs are bangers. They move fearlessly with purpose and meaning. “Memento” is possibly the best of them, satisfyingly Heavy, but also cerebral and complexity level: Advanced. If this is only Act 1 of their play, then bring on Act 2.