Somebody find me a game series that I would enjoy more than the Metroid series (especially the 2D games). I dare you.
Chronologically, Metroid Fusion for the Game Boy Advance is the final game in the Metroid series so far. The galactic bounty hunter known as Samus Aran was attacked by a strange organism on the planet known as SR388. This organism was later revealed to be called the X parasite. After barely surviving, Samus was dispatched to an abandoned space station orbiting the planet to find out what happened to the crew on board and to the X parasites.
What Samus finds on this space station, the Biological Space Laboratories, is a completely abandoned facility, with the exception of plenty of monsters, and X parasites all over the place.
This is a game that I loved since almost before I ever bought it. The actual story of how I bought it is interesting enough. I had to go through at least 10 different GameStops before finally finding one that had the game—and the store that finally had it was actually the one that I looked in first.
But that was, say, six months ago. I got about 3/4 of the way into the game before, and then got stuck. Here I came back months later and restarted, and this time I got through the game.
Why do I love this game so much? So many times you get struck for hours and don't know what in the world you're supposed to do, and then once you figure it out, you gasp at the ingenuity of the developers. When you get to a place where you have no clue what do to, it feels so good when you figure it out. For this reason, I would recommend you not use a guide at all for this game, even if you can't figure out what to do for, say, ten hours. The reward feeling you get when you solve the problem is worth it.
I loved the story of this game, I loved the characters (however very few there were), and I loved the progression. Throughout the game there is creepy music in places where it ought to be, making the game actually creepy. The bosses are impossibly fun, and by the end you start to get happy when you die while fighting one (because it means you get to fight it again).
There are a few minor downsides, such as not being able to explore the ship more with all of your recovered abilities once you beat the game, but the awesome parts of this game outweigh the downsides so much, that this game deserves a solid 5/5.