Metroid 2 was the most linear game in the series
I'd say Metroid Fusion was the most linear game in the series. Metroid 2 at least allowed a little exploration, Fusion was all mission after mission. I'm not to fond of Metroid 2 even though it was a major step in game design leading into Super Metroid (I find the controls sticky, the fact that if you run into a boss fight with no missles you're burnt, and the cut and paste backrounds to be confusing and way too easy to get lost because of), but Fusion was a fun follow up to Super Metroid with impressive graphics that I consider better than the newer game, Metroid Zero Mission.
It amazes me that this horrible of a game has lasted this long.
It's because millions of people don't share your opinion. Except in Japan where it's not as well received as it is in the West. (They say it's because of cultural differences, Japanese gamers like to be told what they have to do and feel uncomfortable in more free form situations. This is why Japanese RPG's are so linear compared to American RPG's.)
Metroid is perhaps my favorite video game series, even over Wing Commander, and it's one of the only reasons I own a console. I love the exploration and and the game's detatched feeling. Super Metroid and Metroid Prime are considered two of the greatest games of all time so there's an obvious reason why the series is still around and is basically nintendos flagship title (at least until the new more realistic Zelda game hits shelves.)
No, Metroid is not for everyone, not every gamer likes to have to explore and backtrack and figure out puzzles and scavenger hunt for their items, all at a much slower pace than other games, especially other first person games. But to many of us, Metroid and especially Super Metroid is like a fine wine that gets only better with age. The Metroid Prime games astonishingly capture the feel of the old games while giving us lush and beautiful environments to explore with incredible attention to detail and environmental effects. Metroid Prime is also one of the few 3D games in which the entire world was constructed so that every area is unique and no game constructing tile sets were used.
Anyone can hate the Metroid series all they want, but there's no denying that Metroid is a classic series that has made a huge impact on the video game industry.
Okay... I'm done ranting now... just can't stop myself when someone badmouths Metroid or Wing Commander.