The gameplay of Indigo, as always with Knizia, is deceptively simple. Players add tiles in turn to expand the routes on the board and gems travel those routes until they land at the outside of the board, rewarding the players whose control markers are there. A few little wrinkles, though: certain gems are worth more points than others and players share the spaces on the outside of the board. So if you connect a gem to your wall, you'll often be awarding another player with the same points as you. Of course, if you must you can just crash the gems into each other so no one gets the points, which will cause many groans and objections from the other players.
Because the points remain hidden till the end and players often share the points, the game causes quite a bit of haggling and harassment considering how short it is (~20 minutes). It's not deep by any stretch but the games I've played have been quick and nasty and interactive. And of course, since it's a Ravensburger game, it's lovely to look at as the routes on the board expand. Definitely recommended if you're looking for a fun, nasty filler and thought Tsuro could have been just a little bit smarter.