Definitely go with Zero Mission instead, if you haven't already tried it. It is much easier for newbies as well as franchise vets to access. (Like Fusion, it puts way-points on the map to guide players on where to go next. Unlike Fusion, activating those are optional, as is the "proper" sequence of item progression.) Metroid 2 is worth a shot if you want to go old school without getting too antiquated. (You can at least shot downwards in that game!)
NES Metroid was similar to NES Zelda. Players were supposed to spend hours exploring the game and ask their friends what they found out from their own experimentation, in order to help each other out. (Also, this is during the "Nintendo hard" era, where if a game wasn't dishing out cheap shots constantly, it was cryptic like these two games.) The only differences were the lack of an included map for Metroid (not that Zelda's map was super) and it was a sci-fi sidescroller. Also like NES Zelda, it is very archaic compared to later games in the series and today is only worth looking at if you're interested in how the franchise began or wish to say you've played all of the games.
I've played through NES Metroid maybe 3 full times. That is compared to Super, ZM, Fusion, and the 3 main Primes, which I've played way too much.