Some things never change. Sometimes that's a good thing.

Since the first game launched on the Nintendo DS in 2007, the Professor Layton series has been one of the best reasons to own a Nintendo handheld. The games artfully blend puzzle solving and an ongoing whodunit narrative into a fantastic experience that has spawned six games, a mobile spin-off, and even an animated film. This week Professor Layton and the Azran Legacy is launching on 3DS, a game that closes the loop on the series' second trilogy. It exemplifies everything that's great about the franchise: it tells an engaging story, is filled with wonderful characters and challenging puzzles, and features absolutely beautiful art and animation. The continued adventures of a puzzle-loving archaeology professor from London and his young apprentice are nothing if not charming. But, in terms of how it plays, it's almost identical to every other Layton game before it. Across six games and two platforms, the series has barely changed at all.

So why can't I stop playing it?