The single player is a drag, but the multiplayer saves this game.
The single player has you playing as Samus Aran. You get dumped on a planet, keep all your powers (morph ball, morph ball bombs, charge beam, etc.), and explore. Now, in the beggining everything is fun, but it gets repetitive after a little while. You have to collect 8 octoliths, 2 on every planet. There are four planets in total, and 2 teleports available. Now, the game only has two bosses, a wierd eyed thing, and a totem pole. You have to fight them both about 4 times. Once you beat one, you get an octolith. After you get the four planets, you get new weapons. These new weapons allow you to go further on every planet. There are new areas in them, and then you return with all 8 octoliths to one of the planets. It can get a little confusing, but there's an ingame map thats extremely easy to use thanks to the touch screen. Overall, all the backtracking really takes away from the experience, and if you go on a planet with your rivals on it, you'll have to face off in a small battle. Sometimes the battle arenas can be very cramped, which is unfortunate. If there are a lot of enemies in a large area, the game will lag a bit. Overall, the single player is short, a bit repetitive, and involves more backtracking then the original ones. It's certainly not as fun, but that's not the real reason to buy this game either.
The multiplayer is absolutely incredible. To heighten the experience you can choose from all the hunters you meet in the game, all with their own useful abilities. Trace is for people who are stealthy, while samus is for people who like using missles, or are good at fire fights. While the game is spoiled with alt abusing, it's still ok, and you can master it yourself if others do it. Every person you meet online will have a different approach in battle, and a different style. Others will jump a lot, and others will run away to get more health or supplies to starve you with none. It's all very interesting, and a brutal battle to get the most kills. This is a lot of fun and is never particularly aggravating. The win/loss system is also a lot better, which is in the form of stars. This can allow you to match people with your own skill, but it's a shame because this system is a little faulty, and you'll end up facing someone who's much much better then you. However, facing them will make you better faster. The multiplayer has single card, multi-card, and wi-fi internet. It's fast paced, and never lags, except for the biggest courses. It's improved dramatically from metroid prime 2, especially without locking on.
The control scheme is a little different from the original. However, with some practice you'll get very good, and it's suprisingly fast. You'll prefer this control scheme, because it's very easy to get usd to, and you don't have to rely on locking on. It controls like a mouse, and is an overall improvement to the metroid prime series.
The audio for this game is ok. There are different songs for most areas, and sound like the classic themes. It's been a bit dumbed down, but it's still there. You won't find yourself getting into the music a whole lot, but if you just listen, the music sounds similar to all the past games. The music isn't very good because of all the things in the game itself, but is ok.
The graphics for this game are phenominal. The best on the DS to date. There are many different animations in the game, and they all animate well. You can even see if someone is charging a blast. There are a lot of different areas. It really pushes the DS to the limit, and are obviously the highlight of this game. The areas all look familiar and great. It's not that pixely close up either. The hunter models all look really good too.
Overall, the game is worth getting if you have online wi-fi, but a little less if you want a good single player experience. Multiplayer is competitive and fun, and the single player is good for honing your skills a little. It's worth picking up, and is a good game in most places.