Returning players need not pay any mind to the Deathinitive Edition, especially those that already consumed its additional add-on content. That said, those that have yet to step into the shoes of a Horseman of the Apocalypse and are seeking a solid action-adventure RPG need only to knock on Death's door.
While two of Sublevel Zero's primary features (permadeath and procedural generation) tend to do the game a disservice, its moment-to-moment gameplay stands as something unique enough in the current FPS landscape that warrants at least a look. However, the incongruous nature of permadeath and procedural generation in the game doesn't necessarily make Sublevel Zero a game worth returning to for very long.
An interesting mechanical conceit that does little to build on itself.