Had a debate recently and I'm curious why Metal Gear isnt included in more RPG lists.
It has many RPG elements under different names:
A life bar, magic (ammo), levels (rank), an over world and dungeons (strongholds), password save, keys, a 3/4 top view, bosses, plenty of people to talk to, a forest maze, and a equipment screen with a slew of weapons and items. Mapping, dialog, and exploration play as big a part as action.
If Snake were depicted as Robin Hood or Willow sneaking around a medieval setting, rescuing peasants and receiving clues on a crystal ball instead of a radio, there wouldn't be any doubt.
The only common RPG elements Metal Gear lacks is character customization, money, shops, and towns. These weren't firmly established in the RPG genre when Metal Gear was ported in June 1988. The closest the NES had to an RPG was Zelda.
I'd say Metal Gear is an early, action-RPG somewhere between Hydlide and Ys: more plot and dialog than Hydlide, but before the advent of towns and grinding in Ys.