It's not bad, it's just majorly disappointing.
Metroid Prime 3 is probably on of the worst Metroid games yet. It's not bad, it's just disappointing, because many features and items are not available unlike previous games, and especially after 10 years of getting it right.
First thing is that the game starts in a Galactic Fedration Ship. It looks too much like the beginning of Halo. Suddenly, Space Pirates attack the vessel, and three hunters; Rundas, Ghor, and Gandrayda, investigate other planet's Aurora Units, supercomputers, for a virus that was spread before. The virus corrupts the AUs with Phazon. The only problem with this is that you're forced to know what the story is. Prime 1 just had you starting to play. Prime 2 gave an objective, but no opening story.
The original and natural way was to scan in certain spots in the game to get data. You can still do this, but it is completely pointless, because on each of the planets have a story to them, but it's not very interesting or important. Perhaps Bryyo (a planet) is, but it's just not very interesting.
Instead of areas on a planet, you go to a few different planets. This is a good excuse for putting different themes (like a fire area, a water area, etc.), but on one planet, there's a jungle, fire area, and ice area. To view this on the map, they put it on a Galaxy Map and then you press on a planet. It will zoom in on and you can pick where to view via a landing point (I'll talk about that later), and then you can control the map like before. However, the map is oddly in a smaller area of screen, and can be a little frustrating to view.
Also, the map has a room view feature. Pressing on a room will allow you to view the room without any bordering rooms. There's not much point besides marking a room green. This does seem a little pointless because if you need to know where to go, you have to open up the map, as on-screen, the map won't display marked rooms. Also, all of the tasks in the game are put in the logbook. On the detail screen, there's a button which points to the room on the map it wants you to go to. Marking a room also requires you to unmark it manually.
Pause the game with the 1 button, and the logbook will appear. You can access data you've scanned from lore and enemies here. You can also view equipment details, and the map, and change options. The map, however has to be opened this way, rather than pressing Z. Also, in the options, you can turn the hint system (if on, the game will tell you where to go) on or off. The thing is that you will get people to talk to you about what you have to do anyway. If it's on, they only force you to view which room to go into. This spoils it very much.
Controls are using the Control Stick on the Nunchuck to move (moving like in Prime Hunters), and pointing the Wii Remote at the sides of the screen to turn in that direction. Z will lock on to targets, and B will jump. Moving to the side and jumping while locked on will jump dash. A shoots and holding will charge the shot. Down on the D-Pad will fire missiles, and holding will allow you to lock on to 5 targets with the seeker missiles. The - button will allow you to point and pick a visor to switch to, and the + button will allow you to go into Hypermode. The Nunchuck is also used for the Grapple Beam.
The HUD has been changed to a hexagonal design. This is odd, because Samus's suit was changed slightly in Prime 2, but her HUD was the same. In this game, the suit is the same, so why is her HUD different? Also, there is no on-screen weapon change or radiation meter, which makes a portion of this look useless.
The on-screen weapon change is gone because the weapon change is gone entirely. There are only three beam weapons in this game, and they all overpower the previous. This means that boss battles and puzzles can't use this to challenge the player. The first beam, the Power Beam, is a standard shot. The second beam, the Plasma Beam, comes back from Prime 1, but only improves from the Power Beam by burning some objects and enemies via a charged shot. The third beam, the Nova Beam, allows Samus to shoot through liquid Phazon as well. One thing that's odd is that the Plasma Beam has the Arm Cannon (Samus's gun) tomorph with the top raised. This is the same as the Ice Beam in Prime 1. Prime 1's Plasma Beam was sticking out at the front.
Items that return are the missiles, the seeker missiles, the Morph Ball bomb, the Boost Ball, the Spider Ball, the Grapple Beam, the Screw Attack, and the X-Ray Visor. The Morph Ball is back with all it's gadgets, except the Power Bomb, which was in every Metroid game since the SNES game. The missiles are back as well as the Seeker Missiles. The Grapple Beam has been split into three categories. The first powerup allows you to rip off magnetic surfaces such as some doors and shields. The second allows you to swing like before. The third allows you to give and take energy to machines to turn them on or off. This seems very odd to collect three parts of a power-up. The Screw Attack is back, even though that the A button won't allow you to stop doing it instantly (I don't know why). The X-Ray Visor has also changed. It's basically Prime 1's Thermal and X-Ray visors together.
You start the game with the Charge Beam, Varia Suit, Space Jump Boots, and Morph Ball. One thing which is completely stupid is that since you don't lose your items alike the previous 2 games, why does Samus not even have the missiles? It's always the first item you get, and she already has the Space Jump Boots. Another item which Samus doesn't get is the Super Missile. Energy Tanks are back, and a new expansion pack called the Ship Missiles.
Samus's ship is different (again) and it is designed like a battleship, with lasers and all. You can get a Grapple Beam and missiles for the ship. These can only be used in certain points in the game, and when you might want to bomb all the enemies, you just can't. A new visor is the Command Visor, which allows you to get your ship to use all of these powerups or land. You scan a point somewhere, and then the ship will do the action that you scan. You can get the ship to land at any landing point in the game as you discover them. You can save your game at each of these points and fly to each other (defying the elevator system). This makes it not seem like the world is vast and large. It also makes the game not have many save points (there's 8 in total).
Suits are limited, because there's only the PED suit (which isn't as cool as the Varia Suit), and the Hazard Shield. The PED suit is obtained shortly after starting. After Dark Samus blasts you with a powerful Phazon attack, making your body self-generate Phazon. This will allow you to use Hypermode (and nothing more). The Hazard Shield allows you to walk in the acid rain in the Pirate Homeworld. These create a cool orange force field around Samus.
Hypermode allows you to use a Phazon attack that is very powerful. The only problem is that you use up an entire energy tank (unless you don't use all of it). After 10 seconds, you will make lots of Phazon increasingly, and you have to get rid of the Phazon, or you'll die of terminal corruption. It's a good idea, but sometimes, you won't have an energy tank, and you'd be stuffed. Sometimes you'd fight a boss, and you don't have enough energy, so you're stuffed. Some enemies also go into Hypermode and use Phazon, but they die quickly with Phazon.
The worlds aren't completely varietive. There's one planet which is covered in dangerous clouds so there's a base built on top. That's pretty sweet, especially since it loads this in 10 seconds. The other planets aren't as cool. Loading times take about 10 seconds, which is slightly longer than before, but the detail is just as good as Metroid Prime 2. The game's controls aren't bad, but using a GameCube controller could have been better. Also, the graphics just weren't improved. Prime 2 had better than Prime 1, but I guess it would have been hard.
The game loads when you shoot a door, without saying loading, but if you skip a cutscene, the game takes a second in a black screen with Metroid Prime 3 in the bottom-right. Also, travelling across landing points takes a while, and is boring during the process on the same planet, because the ship is there and that's it. Between planet's the ship flies around a bit.
Sound design isn't the best either. The music could have been better, because none of the tunes are extremely memorable. Gameplay is lacked a lot. In fact, you could replace the Phazon with the X parasite, and you could call the game Metroid Fusion 2. The gameplay is too linear, and overall, it's not the best Metroid game out there. It's good, just disappointing to Metroid fans.