Phantasy Star 4, Lunar: Eternal Blue, or Final Fantasy 7 for me.
Whenever I rented a regular side scroller beat 'em up type game that it was too easy to play through and finish in no time, whereas with the JRPGs I could go on for 50+ hours, which as a kid seemed like such a great thing.
Lunar: Eternal Blue in particular seemed pretty cool though with how its dungeons were setup. Playing on a ROM more recently kinda showed me just how disorienting an effect random battles can be especially when coupled with a dungeon with paths that wind around. Made it seem a shame that when they ported the game from the Sega CD to Playstation that they cut out the random battles for stationary mobs that initiated fights as well as simplifying the dungeons.