While it may be slightly cumbersome at first, once you get into it, everything about Metroid Prime feels very natural.
The bounty hunter Samus Aran has just received a distress call from a nearby space station, and having arrived, she soon discovers that the Space Pirates are up to something dastardly, but before she can discover what they're up to, the station self destructs, but Samus escapes to the nearby planet of Tallon IV before the station is completely decimated.
Upon landing on Tallon IV, Samus soon comes to terms with an entire planet corrupted by a toxin called Phazon, which arrived via a meteor, and soon after collision, everything was poisoned, and the peaceful Chozo race who once used the planet for research had to flee. What does become apparent soon enough is why the Space Pirates, and Ridley, are on Tallon IV to begin with, and how they're profiting from the misery and destruction brought by the Phazon.
Metroid Prime is a radical departure from the rest of the series, in that instead of being played from a side on, 2D perspective, the entire games in now played in the first person, behind Samus' visor. In essence, Metroid Prime is now a first person shooter, but with a lot of inspiration from the adventuring elements of yore.
When first entering an area, Samus will be alerted to an environmental disturbance in the vicinity. You'll have to get to that point using all of Samus' abilities, and once there, there'll usually be a boss fight, and once the boss has been defeated, you'll gain a new ability which will enable you to traverse the further hidden depths of Tallon IV.
Along with the discovery element of the gameplay, there is also the combat, which has been done surprisingly well. There is a slight learning curve to the combat, as Metroid Prime employs a unique control system which is vastly different to that of any other First Person game. All movement is done with left stick, and if Samus wants to look up, you must hold the R trigger, and that will have Samus push her arm up to look. It may seem a little slow at first, but the lock on feature, accessed with the L trigger makes it far more user friendly. The combat itself is great fun, and with Samus being able to move at quite a brisk pace, she's able to expertly dodge all sorts of dangers. These dangers come in the form of the many mutated creatures that now inhabit Tallon IV. Their A.I. is ferocious, and they offer a challenge regardless of how well versed you are in their behaviour.
Tallon IV is made up of vastly contradictory areas. The snowy shores of Phenandra Drifts present a calming, idyllic winter paradise. The fiery core of the planet that is the Magmoor Caverns present a burning world of technology that is slowly rotting away. Those are the two that stick out in my mind the most, but the other districts have their own appeal, and together the areas come together to create a living, breathing world which immerses you from start to end.
There are various graphical touches, such as the extraordinary lighting at the save points, and dust covering your visor, which help to make Tallon IV even more realistic. The rousing soundtrack emphasises the mythos of each area, and so you are truly drawn into the decaying former paradise that is Tallon IV.
You can expect to devote a good 40+ hours into Metroid Prime, as there's much to be seen, and in order to discover everything the planet has to offer, you'll need to do a lot of exploring and thinking as the path forward is rarely obvious, and only through clever use of your abilities will you be able to push on. There's also a fair deal of backtracking, but any boredom is alleviated through your new abilities allowing you to discover brand new areas on the way back, and new health and bomb upgrades to boot.
Closing comments: Metroid Prime is a fantastic return for a series that was in dire need of one. Metroid Prime reinvents the Metroid series as well as Super Mario 64 and Ocarina of Time did for their respective series. From the minute you touch down on Tallon IV to the moment you'll finally have to say farewell, you'll be entranced by a world that has been so finely tuned and polished, and gameplay that, while being a tiny bit cumbersome to begin with, quickly becomes second nature thanks to its ease of use.