So, a word of warning and caution - this post MAY contain minor spoilers. To best explain and review the game itself I have to be able to talk about plot points to a small degree. I'll keep it very vague and non-spoilery if I can.
For several years I've played the Metroid games. They've always been interesting and fun for their gameplay and atmospheric immersion, but you had to turn to various manga sources to find out a little bit about Samus' past. Her motivations, her reasons for being a bounty hunter --- some of these are explained to a degree, some of these are implied.
Spoiler time, but not really dealing with the most recent game - Other M - itself. In the official Metroid manga we learn about Samus' past, youth and time under the Chozo elders, time with the Federation and a CRUD load more. It's licensed, so I can't provide a link, but if you're interested in learning more it's not too hard to find. Suffice to say, it has a LOT of back-story that helps in understanding some bits about Samus' character.
That's not to say her characterization is exactly consistent. Her manga persona is almost care-free at times, whereas Samus-in-game(s) is mostly serious about the work she's doing. This slight disconnect isn't a big deal when you consider that a good portion of the first volume takes place prior to the original Metroid game and the manga as a whole becomes a sort of coming of age tale for her as she learns, grows and fights towards the events of that game.
Major things about Samus that you should understand:
Samus' birth parents died, killed in a raid on a research outpost conducted by Ridley. She met Ridley when she was a child, about 3 or 4 years old, and he spared her life at that point. She was taken in and raised by the Chozo as one of their own, underwent a bit of adaptive genetic manipulation to make it possible to live long-term on Zebes, grew up and learned to fight. She left after that point, went to the academy, faced her tenure under Adam Malkovich, and left there after a time to become a lone bounty hunter.
Other M does this established past both justice and adds a decent amount of useful exposition, providing deeper connections between Samus and other characters. The story itself is passable, if a little hard to swallow at times... I found one of the most interesting facets of how the story plays out to be the little white fluffball creature and what happens to it.
That definitely doesn't mean the story in uninteresting, but... well, just play the game and you'll likely see WHY I like the creature's subplot so much.
The rest of the story is interesting in its own ways - Samus is far less clinical in her interactions with others, showing genuine emotion when those around her are facing danger. Unfortunately, this means she faces the occasional freeze-because-some-past-traumatic-event-is-causing-me-to-be-terrified thing. Samus HAS a past... she has a history with the GF soldiers she meets right at the beginning of the game (minor spoiler al--- aw, whatever) and most importantly that history involves Adam Malkovich. In the games themselves, Adam was introduced as an A.I. character that guided Samus through the research facility where the X were running rampant... the events of Metroid 4 (Fusion)
Other M steps back to a time when Adam was still alive.
I personally feel that Other M does the series as a whole a great amount of justice. So many reviews complain about how it's not a Metroid game because of one thing or another. Nonsense. It's faithful to the character of Samus, and says a whole lot more about her than a simple cookie-cutter sequel to the original 2D games would. It shows that - despite what she has faced and no matter how hard things have been - she is still human underneath her armor. If you don't like that Nintendo has tried to take steps to make her easier to relate to, then I say 'get over it! Seriously!' because if any character needs a solid voice, it's Samus.
She's the center of a very large science fiction based universe, and there are still a lot of questions left to be answered... let's let Nintendo decide how they want things to play out and just enjoy the ride.