Pikachu is normally very cute and a little bit sassy, but its Detective variety is unlike any Pikachu you've ever seen. Detective Pikachu plays with your expectations of what Pikachu should be, and the game has a lot of fun reveling in the weirdness of a small, adorable creature talking and acting like a human man. It's campy and self-aware, showing a different side to Pokemon and Pikachu with an infectiously rambunctious attitude. Detective Pikachu--the character and the game--is full of personality, and as a result an otherwise standard mystery-solving game is far more fun and entertaining than you might expect.
You play as Tim Goodman, who has arrived in Ryme City in search of his father, Harry, who went missing in an accident. Of course, the real star is Detective Pikachu--you meet him almost immediately, and you're the only human who can understand him. Like a grizzled detective out of a '50s noir, he sounds like a middle-aged man and gestures like a caricature of a New Yorker, and his voice acting and animation captures that character perfectly. He'll occasionally get your attention with a cute jump and a gruff "Hey!"; sometimes he'll give you hints, which are entertaining even if you didn't need them, while other times he'll just chatter away about something random or interact with a nearby Pokemon. His streetwise attitude and campy quips never get old, adding a delightful (if weird) charm to every scene.
You soon learn that Pikachu was your father's partner Pokemon and lost his memories after the accident, though he can still lend you his detective skills to solve mysteries. Those mysteries largely involve misbehaving or even violent Pokemon, most of which have been exposed to a chemical called R. The cases start out with simple mischief, but as you investigate, you'll solve bigger ones--including actual white-collar crimes--and find clues about Harry's disappearance. The game follows a basic detective story structure overall, but the pulpy tone can make it feel less derivative, and the conspiracies around R and Harry are intriguing enough to keep the pace up.
Cases consist of everything from finding missing Pokemon to whodunnits with dramatic reveals. Your job is to talk to people--Pikachu will translate for Pokemon witnesses--and gather evidence that you can then use to solve each case. You talk to people, get more information, and use that information to unlock follow-up questions until you have everything you need to start the deduction process. Pikachu guides you through most of this, framing the questions you need to answer and later prompting you to pick the evidence that best supports your theories. There's no real way to fail; as long as you talk to everyone and search the environment thoroughly, you'll get everything you need to piece things together. That on its own is disappointing if you're hoping for compelling mysteries and puzzles.
Finding all the clues is fun, however, especially with Pikachu wisecracking as you go. Getting one solution will open up a new question or pose another problem to solve, and while they all follow the same gameplay structure, each case is deeper than it seems at first. For the most part, I was never so far ahead of the game's pace that I was still gathering evidence long after I'd figured everything out--while nothing shocked me, there were times when I wasn't entirely sure how a culprit had done it until I was choosing what evidence matched Pikachu's hints. But there were also a few frustrating times when I'd figured out the solution but couldn't find the last piece of evidence to back it up. In one chapter, for example, you have to gather a half dozen or so alibis, then use witness testimony to deduce which alibi is a lie. It involves a lot of talking, and I ended up running around for 15 minutes re-interrogating everyone until I finally found the person I'd missed (despite knowing who was responsible and why the entire time).
It's hard to stay annoyed for long, though, because Detective Pikachu is brimming with personality. Pikachu himself is a total goofball, but the other Pokemon are also entertaining in their own right. Each one gets its own special subtitle (Garbodor is the "connoisseur of trash," for example), and they typically have interesting things to say, even if those things aren't useful as evidence. The world of Pokemon is cleverly incorporated into different parts of the New York-inspired city, from flying Yanma that work as news camera operators to the Trubbish that occupy the subway entrances. You don't need to know anything about Pokemon to solve Detective Pikachu's cases, but being familiar with Pokemon and appreciating all those details enriches the simple gameplay and story.
And Detective Pikachu is a simple game. There's not much variety to the way you solve cases; the story follows a standard detective formula, and as long as you're thorough, you won't have too much trouble connecting the dots. But it's full of heart, and its silly characters and intentionally campy tone are what make it fun.