One of the most surprising board games that I've ever played was Atlanteon.
In Atlanteon, each of the players takes turns playing a single piece onto the grid-shaped board. They each have pieces numbering from 0-9 as well as a king piece (and there are 3 towers that are placed on the board to start the game). Whenever a piece becomes completely surrounded, then it is scored; to do this, each player adds up the total number of points they have adjacent to the piece (and the piece itself), and whoever has the higher total scores that piece (except with one of the towers that scores by the lowest total). This continues until one of the three victory conditions is met: 1) a player's king is captured (this rarely happens), 2) a player has scored 11 pieces and has his king on the board (the most common scenario), or 3) one player has captured all three towers (this also rarely happens).
The first pro of this game is the ease of teaching new players, and yet the depth of gameplay. Like Othello claims to be (but Pentago actually is), I consider Atlanteon to be easy to learn but difficult to master. Within a couple minutes, you can teach a new player how to play the game. Mastering the game will take much longer (in fact, I've played it quite a few times and I'm still lousy at it). More than any other game that I've encountered recently (except for maybe Yinsh), I think that Atlanteon balances these two characteristics spectacularly.
The next pro is that I like the different victory conditions. I'll be honest - two of the victory conditions have never happened in a single game that I've played. I've never seen someone's king get captured, and I've never seen someone capture all three towers. However, just the fact that these things can happen is enough. If the only way to win were to capture 11 pieces, then the game would be much easier to master. Having to ensure that you don't let the other player take your king or the towers forces you to play in certain ways that may prevent you from being able to capture as many pieces long-term (because you have to prevent yourself from instantly losing).
The only real con that I've found for Atlanteon is that it will live its life as a filler game. Since the game only takes about 10-15 minutes to play, I have a difficult time imagining people getting together specifically to play the game. (However, it is still a wonderful game for playing while you wait for the member of your group that is inevitably late. Doesn't each group of gamers have one of these? Or 4 of these?)
Overall, I give Atlanteon an 8.5/10. I really like this game. However, since my personal rule on rating (until I change my mind in a few days) is that I won't give a game a 9 or higher unless I can see myself getting together specifically to play the game, I can't rate it any higher. Either way, anybody that likes games like Chess or Hive should definitely try this game.
If Atlanteon sounds interesting, you might also check out Architekton, Gipf, the Innovation card game.