I really enjoyed this game, not as much as MP1 or 2, but still thought it was really good. The graphics look real nice and each area you visit has a unique look to it. There's a lot of exploring to do as this is easily the longest of the three prime games. The music is good but subtle. There isn't any music I would say was great but it does fit the environments.
Controls - The game controls fairly well using the wii controller. It takes a little while to perfect turning your vision by placing the cursor to whichever side of the screen you want to look towards. That said, I never had any problems with it. I also never had any problems moving about or jumping. Occasionally for some reason my rounds would skew off from where the cursor was on the screen, so I'm not sure what that was about. It only happened rarely and didn't cause any problems or anything but it was noticeable when it was happening. If you want to use the multi-missile lock, you had to waste a missile before you could start locking on to enemies. You get a ton of missiles in the game so it's not a big deal but it's a slight annoyance. I really liked the control scheme for MP 1 & 2 and I really don't think the controls for this are a huge improvement like a lot of people seem to say. I like them both about the same.
Environments - Plenty of different environments in this game as you visit 5 different planets and a ship. My only real complaint here is that in order to visit different sections of planets you have to go back to your ship and then fly over to them. Later on you can connect some of these sections together so you don't have to fly but there will still be some sections of planets that are completely separate. You'll also be flying around all these different planets and sections a lot so you'll have to watch plenty of flying sequences. Unlike most other Metroid games, you will be in contact throughout the game with an AI unit and federation troops. The dialogue isn't overly heavy and it's not cringe worthy. Just don't expect anything great. You'll still fight alone, except for one sequence, but the game doesn't have that sense of being all alone on a mysterious planet. It's not necessarily a bad thing and the change is nice. As long as this doesn't become the norm, I'll be happy.
Upgrades - There's 100 total upgrades to be found during the course of the game. While most of the suit upgrades add new abilities to let you explore new regions, the non suit/ship upgrades seem really limited. You'll find Missile expansions, energy tanks, ship missile expansions and energy cells. Pretty sure that's it. Outside of the beginning, you'll never run out of missiles at any point and most of the upgrades found will be these. Missiles aren't quite as useful in this one either as you won't use them too often on bosses. I figured the ship missile expansions were for some sort of space battle towards the end but there isn't one. After I finished the game I read that you could actually call in your ship to fire these in open areas to kill enemies, had no idea so I never used them other than to blow up stuff for mission progress. Still, they seem like a fairly useless power-up to find. The energy cells are just used for a fetch quest later on to open doors on a derelict ship to find something you need to complete the game.
Because the wii is limited in buttons, you can no longer switch between cannons. When you find a new one, it just overrides your old one. It's not a huge deal but I missed being able to switch between cannons for certain situations. The only thing you can really switch between is visors. Skytown has an observatory that will launch a probe for each planet that puts a white dot on your map to show you where upgrades are located. This is convenient if you're a completionist or for when you're forced to find the energy cells. The new hypermode adds an interesting dynamic in that it uses your life for more power to your weapons.
Enemies - There's plenty of enemy variety. Some enemies you need to grapple to kill or to remove shields they're carrying. This can make fights a little more frantic when you're being blasted at while trying to remove the shield an enemy is using to block your fire. The thing that annoyed me the most is that most enemies can go into hypermode just like you. They then fire significantly faster and do much more damage. I don't mind the increased damage that they do but they also get a huge boost in damage reduction. It takes forever to kill a normal enemy with your cannon and missiles if they go into hypermode. Unless you enjoy putting 40+ rounds into the guy, it is just much less annoying to go into hypermode yourself. This of course forces you to have to use your life to kill them.
Challenge - This is where this game annoys me the most. The game isn't very difficult and I played on hard mode during my gameplay. Skytown itself is a complete breeze as there aren't many enemies and the ones that exist there are really weak. The only real challenge is making sure you don't waste too much of your life in hypermode. The bosses in particular make this a real annoyance.
The boss fights in this game are moderately long. I didn't mind this at all but most bosses will take about 7-10 minutes, maybe more. There aren't really too many boss fights though so it's a nice break from exploring or fighting the regular enemies. I still enjoy figuring out their weaknesses and patterns and exploiting them. The only thing I really hate is that during the main boss fights, you're forced to use your hypermode cannon and use your life to hurt them. Some bosses give back life so not a big deal but there were a couple where I didn't get any life back during the fight. Most of the damage you end up taking won't be because the boss is messing you up but from being forced to use your life to damage them. This led to a couple close calls during boss fights where I wasn't sure I'd actually be able to kill them because I'd made myself run low on life. I didn't like the forced difficulty coming from forcing me to use my own life to kill them. The final boss fight is pretty decent. Came close to dying during the third part of the fight but pulled it out.
I only died once during the course of the game against a mini-boss who was a red phazon pirate commander. I went in with about half my total life and this guy takes about a million rounds. I must've done 600-700 damage to myself just blasting him with the hyper cannon but he just wouldn't die.
Minor quibble - Sometimes you'll shoot a door and it'll take 15 seconds for it to open. Doesn't happen often but there are certain doors that will almost always do this.
I had fun playing the game and it never boring. There's plenty to explore though you may get tired of going through the same environments over and over again, especially Skytown. The boss fights, while fun, were somewhat overly long and tedious in that I was never worried about them killing me but about me killing myself. I wish the game was harder without having to rely on me killing myself in hypermode. Having to constantly run back to the ship to fly to some other section or planet gets tiresome after a while, especially the loading. I wish there'd been more missile/cannon upgrade types to choose between and more regular upgrades that were worth getting other than energy tanks. Overall, I'd give the game an 8 out of 10.