This original take on the Metroid series fails to deliver the pace and gameplay of it's predecessors.
Based on pacing, the Prime series of Metroids were slow in comparison to the original 2D iterations. Other M's pacing is equivalent to Prime through the majority of the game play but slows to a crawl at awkward moments when (seemingly for dramatic effect) you're forced to go to an over the shoulder mode that makes Samus move at a slow walking pace (sometimes through large areas). Other points the game grinds to a halt when the game changes to first person view and forces you to stand in one spot and survey the scenery for a particular object without giving you any hints as to what you're looking for. These moments can be frustrating and often kill the pace of the game entirely.
The game shows you where the power-ups are on the mini-map but this often frustrates you more than anything as some items appear like they should be obtainable at that stage in the game but at times it's hard to see what places in the room are things you can stand on and what's merely decoration (a problem rarely seen in any other Metroid games, which make the distinction clear). Often this results in you spending 10 minutes trying to figure out how to get an item before giving up and moving on. This experience isn't new to Metroid games, but Other M pits you up against similar situations in virtually every third room.
Combat is more complex than previous Metroids, forcing you to dodge and move around more. Average enemies are also more difficult to destroy. Also, the enemies don't drop any items/energy when you defeat them. This makes the game problematic as you have no way to recover energy until you're about one hit from death and then in order to recover energy you have to use "Concentration" which requires you to stand still for about 10 seconds. If you move before you've recovered, you have to start all over again. If you manage to recharge, you'll only recover a small amount of energy (up to your default 99 energy at first, later you can recover a few extra tanks worth). This makes it so that in difficult boss battles, you'll have to use Concentration more than once and having to stand still for 10 seconds is difficult to do with big bosses flailing their arms at you constantly.
A bigger problem is that enemies hit you quite hard in this game, often taking 50+ energy away in a single hit. At first, you can't even use concentration unless you're below 25 health. The game seems to try to fix this problematic mechanic by making it so that hits that would normally obliterate you will leave you with your energy flickering between 0 and 1, giving you a fighting chance to use Concentration when you'd otherwise have been one shot before having it available. This further seems to make the game feel less like a Metroid game and more like a generic button mashing action title with cheap fixes to help mechanics that would otherwise render the game almost unplayably frustrating.
The controls are seriously wonky as well. The game forces you to use a Wiimote turned on it's side without a Nunchuck. The big problem is that the crosspad on the Wiimote is sub-par and it's very difficult to get it to work diagonally. Additionally, in order to fire missiles, you have to switch to the non-mobile first person view by pointing the Wiimote at the screen. This often results in you having your back to the enemy or facing in some other awkward direction and having to slowly ban around while not being able to move. There are various other control schemes that would make more sense, but Team Ninja doesn't even provide any options to change the controls. You're stuck playing the game as-is.
It doesn't help matters that the game has a serious game-breaking glitch in which running back to save the game after defeating a certain boss makes you irrevocably capable of progressing. It helps even less when you're only option after falling victim to this glitch is to mail an SD Card with your save game on it to Nintendo and wait for them to send it back. That flaw in and of itself would be excusable with an adequate fix and a better game, but this one is frustratingly difficult and departs too far from the originals to truly be worth the hassle.
Of course, there's lots of arguments against the plot. Samus, ever the strong silent protagonist, is portrayed in Other M as a traumatized emotional wreck. For a person that later takes what happens at the beginning of Metroid Fusion without so much as breaking her stride, this seems awfully off-pace for the character's persona. There's also the issue with the fact that Samus has all the upgrades on her power suit from Super Metroid but refuses to use them to the point of death in order to impress her former superior officer, even to the extent of running through flaming areas without her suit's heat protection on until given the OK to use it.
If you haven't played Metroid before, I'd strongly recommend you start with another title. Only play Other M if you are a stubborn/hardcore Metroid fan and/or like button mashing action games.