Despite the surface trappings of a fishing theme, Tonari is a perfect information strategy game in which players take turns moving a boat through a sea of tiles, claiming the tile they move onto and either adding that tile to their collection or using its special ability. When the boat can't move, the game ends and players tally their score.
The twist of the game, which is hinted at in the Nachbarn name, is that in a three- or four-player game, a player's final score is equal to the sum of their points and the points scored by their left-hand neighbor. You might collect the most points in the game, but if your right-hand neighbor has a higher score than your left-hand neighbor, then your right-hand neighbor wins, thanks to them handing you lots of points, you not handing your left-hand neighbor points, or both.
That simple twist drives gameplay in interesting directions, and Faidutti has played it up by adding special action tiles to the game that allow you to swap the placement of two tiles in the game, swap one fish tile with one held by another player, and a double-scoring tile that delivers twice as many points as normal for one standard type of fish.
Unlike Nachbarn, Tonari can be played by two players, and in that case you simply compare points with your opponent to see who wins. When playing this way, I'm reminded of the abstract strategy game Tintas, which I covered in 2016, as that game also has a single pawn that players take turns moving. With three or four players in Tonari, you're fine moving the boat somewhere that profits your neighbor, then zings the player afterwards, but two-player Tonari requires tighter play, with you trying to force the opponent into bad moves, whether picking up a piece worth -5 points or allowing you to grab the fifth or sixth tile in a color to boost your score.
I've played Tonari eight times on a review copy from IDW Games, roughly split between two- and three-player games, and I offer more thoughts on play in this overview video: