Turnabout Improvements.
Mechanically, Ace Attorney Investigations: Miles Edgeworth clearly stands as the highest point in the Ace Attorney series. Though somewhat controversial, many of Miles Edgeworth's changes help to streamline the process of working your way through the text-adventure game's courtroom drama. Rather than splitting the investigation and trial sequences, you'll do a small amount of crime scene work and then listen to testimony. This both speeds up the pacing of the game -- something that the series has needed for a while -- and makes the flow of the game feel more natural.
The biggest change, however, is the switch from first to third-person perspective. While it may not seem like that much of an improvement, being able to move Miles Edgeworth around as he gathers clues and testimony makes the game that much easier, since it's much less difficult to miss an important piece of evidence that might've been hard to see. For the most part, you'll only investigate one area at a time, instead of having to jump from scene to scene, looking for evidence that might not be there. There's also the introduction of the "Logic" system; in addition to finding clues, Edgeworth can collect pieces of information and fit them together to form a conclusion, which moves the story along more quickly.
But aside from the fact that you play as the titular prosecutor instead of Phoenix Wright, Miles Edgeworth sticks to the series' storytelling formula to a fault. A murder -- always a murder -- is committed, and someone is wrongly convicted of said murder. As you make your way through the case, you'll prove that person's innocence, and finally, convict the real killer, who breaks down into a confession and wild spasms once you definitively prove their guilt. There are plenty of the series' signature plot twists, and many of them seem nonsensical at first. You're also usually three steps ahead of the case and know who the bad guy is around halfway through. Though there are times where you'll be randomly presenting evidence because you're completely clueless, I have no qualms in saying that this is by far the easiest game in the series.
I could rag some more about the predictable story of the game, but it's a testament to the series' writing that even though I could spot the killer from a mile away, Miles Edgeworth never lost me. The characters are still ridiculous and comical, the dialogue uses a great mix of pop-culture and inside jokes while never losing sight of the main plot, and when you've made your final conviction, it's always rewarding to see the heated back-and-forth play out. Predictable or not, it's difficult not to get caught up in the game's intricate plot.
Miles Edgeworth is the best game in the Ace Attorney series to "play", but that doesn't make it the best entry in the series (that title belongs to Phoenix Wright Ace Attorney: Trials and Tribulations). That doesn't stop it from being an enjoyable text-adventure game, and one that potential newcomers can approach more easily, even with all of the inside jokes. It could be said that the game plays itself, and it does, but that shouldn't diminish the value of a well-told story.
