Metroid Prime 3 is a great game, but some odd design decisions keep it from the level of its predecessors.
Cons: Some game segments feel out of place; Hidden items are too easy to find; Forced use of motion controls; Save points are too far and few between
Metroid Primes 1 and 2 were both very epic Gamecube titles that spanned the planets of Tallon IV and Aether respectively. Thus, no doubt looking for ways to improve the size and scale of the third adventure, Retro Studios decided to make more use of Samus' ship and expanded the adventure to far more locations. They also decided that there should be more dialogue and combat emphasis on their third title around. As a result, Metroid Prime 3 is a very epic, if not frequently un-Metroid, feeling adventure.
Don't get me wrong with that last statement. There is still plenty of that same Metroid gameplay found in prior entries. You will still be tasked with traveling to many areas and grabbing upgrades to help you proceed further upon backtracking. Combat is still the same as Metroid Prime in a sense, although thanks to some sharp Wii motion controls it comes across as smoother this time around. And you will still fight a variety of exciting bosses that will task you with combining your various moves into an effective strategy. In that sense, the only thing that's truly changed is the greater emphasis on combat this time around.
However, the feel, and occasionally even gameplay traditions of Metroid get pushed aside at multiple points in the game. Start with the story: Samus is called upon by the Galactic Federation to help rid the galaxy of phazon (a hazardous material from the first two games) corruption. While there's nothing wrong with this plot, it ruins the sense of isolation that Metroid is known for when you are frequently talking with members of the GCF and getting updates on exactly where to go next. Later sections of the game in particular have an identity crisis with the two biggest offenders being an escort mission and a cutscene that seems to have taken too much from Star Wars. On a less stylistic note, it's a little disappointing that Metroid Prime 3 succumbed to the gimmicky control trend of many early Wii games. Frequently (read: almost every time you find a switch), you are tasked with using the Wii remote to complete a little key turn movement or solve a mini-puzzle by twisting the Wii remote exactly as needed. These aren't bad, but they feel out of place in a series that previously let you open doors by scanning switches.
Unfortunately that's not the only disappointment. Thanks to constant directions on where to go and some more obvious scan logs it's much harder to just get lost and thus there's less of a reward for exploring carefully. Furthermore, many of the pickups are placed directly in your path to vital objectives, practically given away to you. Again, much like the odd decisions, these disappointments don't ruin the game by any mean (there are still some pretty tricky environmental puzzles), but they do hamper the experience.
Luckily, all other portions of the game hold up admirably. The graphics are great as always, and continue to be among the Wii's best. The art design of the various bosses, the levels (particularly the Sky Town level) is among the best in the series, and the graphics technology has been subtly upgraded to render everything with more detail than before. Music here is also some of the best in the trilogy with perfect mood-setting pieces including an absolutely haunting menu theme.
I know I've ragged on about Metroid Prime 3: Corruption a lot, but the fact still stands: the game is still fun. The things that made the first two Prime games classics are still here, they've just been dampened by some odd decisions. This is still certainly a game worth playing for any Metroid fan looking to finish the trilogy, and this is perhaps even the best game to start with, given the many streamlined decisions.
Metroid Prime 3 is easily the worst of the games in the trilogy, but when the trilogy was so good to begin with, you still get something worth playing.