The Professor Layton series follows an English gentleman solving brain teasers and occult mysteries with his apprentice Luke. The Ace Attorney series follows lawyer Phoenix Wright as he breaks down the logical flaws in witnesses' testimonies to protect his clients and uncover the truth in a court of law. At first glance they might not seem all that similar. But upon closer inspection, they both revolve around one simple concept: challenging your very ability to think. And it is this very reason that Professor Layton vs. Ace Attorney is one of the best crossover games ever made.
Good — True to the Feel of Both Parent Titles
The most obvious potential problem when combining Ace Attorney and Professor Layton is the setting. Ace Attorney takes place almost exclusively at the crime scene or in a courtroom. Layton, on the other hand, often takes place in various isolated and mystical locations. Yet, Professor Layton vs. Ace Attorney overcomes this potential obstacle by picking the perfect setting for both: a witch trial in a self-contained (and quite literal) storybook world. Thus when it comes time to gather evidence, Layton and Luke are free to wander around the city contained inside the book, doing puzzles and solving mysteries. Then when it's time for the trial, Phoenix and Maya can use the collected evidence and revelations to protect their accused client in the medieval courtroom setting. In other words, it is a game that perfectly manages to combine the spirit of both parent series.
Good — Phoenix and Layton vs. God
Professor Layton vs. Ace Attorney is not, however, what the title implies. While hardly seeing eye to eye all the time, Layton and Phoenix are both firmly on the side of the young girl
Mahone who has been accused of being a witch. The villain in the story is actually the "Storyteller," the writer of the book they are in. The Storyteller quite literally controls the fate of all those inside the book. Even those coming from the outside can be influenced to some degree by what he writes once in his world. So in reality, this game isn't really Phoenix versus Layton, it's much more along the lines of "Phoenix Wright and Professor Layton vs. God."
Of course, given the enemies the two of them have faced in their respective series, this "god" might need to ask them for a handicap.
Good — The Mixture of New and Old
The gameplay style of the Professor Layton section is virtually unchanged from the games in the main series. But the Ace Attorney parts of the game now include multiple witness testimony and a spell book (for reference), among several other changes.
While I have only played the first two Layton games and can't make an across-the-board comparison, I found the puzzles in Professor Layton vs. Ace Attorney to be quite good in general as they almost always seem to have a well implemented visual component ranging from picture matching to mazes.
The witch trials, on the other hand, are often on par with the best courtroom scenes the Ace Attorney series has to offer. This comes largely from the handicaps facing Phoenix. He is in a world where he is ignorant of the local laws and customs—not to mention the actual physical laws of a world where magic exists. Moreover, this reality is akin to a medieval fantasy. Thus, the majority of forensic science is non-existent—forcing him to rely on critical thinking more than ever before.
Good — Excellent Presentation
While the Professor Layton games have had voice acting sprinkled through their narratives from the beginning (not to mention an animated feature film), the Ace Attorney games have always been voice free (other than the lawyers' shouted commands of "objection!" "hold it!" and "take that!"). Thus Professor Layton vs. Ace Attorney is the first time gamers will get to hear Phoenix and Maya speak. In the Japanese version, they are voiced by Hiroki Narimiya and Mirei Kiritani, reprising their roles as Phoenix and Maya from this year's Ace Attorney live action film which makes for a great sense of continuity.