Metroid is quite flawed by today's standards, but it was still a gem back then
Metroid is one of those rather tricky classics I can clearly understand lots of the fuss against. I will admit a few things though, it is one of my all time NES favorites, it's more of a product of its era, and time really doesn't help it out. Therefore the negative reception it receives from some gamers really isn't lost on me, because in my view it is overshadowed by pretty much every game in the franchise.
For those who may not know, Metroid is a 2D action/adventure that follows Samus Aran as she explores the lower depths of planet Zebes to exterminate the space pirate leader The Mother Brain. Metroid is among the earliest, non linear exploration games that takes the player through several rather unique areas. I wish that I could play this game again for the very first time as a kid, because I remember being so hooked to it primarily for its sense of exploration. I still get a kick out of now after not playing it for so many years. Every room Samus enters usually looks the same, but there's always that chance of finding some brand new item, as she runs, shoots, and jumps her way to that nearest item leading to victory.
Samus is quite weak when she begins, yet she can be upgraded by various pick ups that does nothing but enhance the game play in extremely noticeable ways; such as getting the ball morph ability and transforming Samus into a ball to reach new areas. Gaining different armory such as missiles and even a freeze way, along with energy tanks to greatly increase health. I would say by the mid-point of this game, Samus will be more than a match for most enemies.
The areas have their pitfalls such as acid and lava pits adding life to the platforming; thankfully these traps only drain Samu's health instead of outright killing her. There are plenty of enemies ranging from easy to mildly tough, plus the boss battles are quite engaging. Although there aren't many boss fights, those that are present will leave an impression especially the final battle which is tough as all hell. The game has an unforgiving difficulty and it sucks to die at really any point, because Samus begins with none of her energy tanks filled, which requires her to recharge each energy tank by killing enemies and this can take a very long time to do. The biggest pet peeve a lot of gamers have is the lack of a real map. Samus will have players running around blind which really can be a pain especially for those use to games with reliable maps. I enjoy those later games the most for having a map, yet this game has its own sinister charm to it in being lost since it works towards the game's immersion.
The graphics were good for their time with there being a difference amongst different sections. Some parts have a good amount of imagination with some platforms looking like bubbled up eggs or something like that. Zebes feels like an alien world all over, and I can imagine a scientist having a field day wanting to explore the place. The soundtrack is catchy and the various worlds have their own tunes which changes the pace a great deal from the main theme.
In closing, I wouldn't recommend Metroid to everyone. I will say that big fans of the series that missed it should give this a play mainly to see where the series came from. To those completely new, I would definitely recommend beginning with Metroid: Zero Mission which is a remake of this game and a damn good one too. Plus, Super Metroid and Metroid Fusion to enjoy the 2D goodness of this series. I'm more than likely going to replay those for the fun of it.
The Good: Challenging with loads of power ups and good boss battles
The Bad: Unforgiving difficulty and lack of map will disturb some players