While I do believe the 8-bit version of Digital Devil Story: Megami Tensei is the platonic ideal—just aesthetically, in every way—it's barely playable by modern standards. If you're interested in MegaTen games—or 8-bit RPGs in general—it's definitely worth experiencing, but watching a playthrough may just be enough. If you're dead set on experiencing the gameplay of an early MegaTen, then start with the Super Famicom.