Mario Tennis Open was developed by Camelot for the Nintendo 3DS, and released to the American market on May 20, 2012. The game features (like most Mario titles) the typical Mario cast, and offers different tennis-based games. The game released with mixed reviews, and unlike previous Mario Tennis titles, there were no RPG elements and no character-specific abilities to set them drastically apart.
The game has a total of 24 playable characters, all from the Mario universe. Only 12 are available for play initially, with four more characters available for unlock during the game and the other eight requiring QR codes. You can also use a Mii character. If you're unfamiliar with what Mii is, the basic explanation is that it is a digital avatar or caricature of yourself that is created by you and used in certain games on the Wii, Wii U and Nintendo 3DS consoles. In this game, it is actually advisable to use your Mii character, as the many customization options made available by purchasing things through the expansive and fun in-game store can't be used on any of the other characters.
In fact, the upgrade and customization options in Mario Tennis Open are a source of quite a few of the problems people have with this game. For example, the statistics of items (such as racquets, hats or shoes) aren't easily discernible; for one thing, the stats are displayed in pie charts (something many major reviewing organizations found absolutely mystifying). For another, you can't see the cumulative effect. While this might not seem too bad, it has the unforeseen effect of making it impossible to actually compare your Mii character's stats against any of the default characters' stats.
That's really a huge letdown, because the in-game reward system has the makings to be great. New things are unlocked for purchase with virtually everything you do (all purchasable with coins earned by playing, of course), many of them stat-altering items that give you a real sense of reward for your work and enhance the replay value of the game. The lack of a basic system for comparison ruins all of that.
One good point about the game is that it is amazingly addictive. The interface is mostly easy to use; you can do different traditional tennis strokes (slice, lob, topspin, drop shot, etc.) with either button combinations or using the touchscreen. Again, though, something positive is brought down by something that doesn't work quite right. The camera must be moved by using the 3DS gyroscope. This entails rotating the console, while playing, to move the camera.
Mario Tennis Open features pretty good multiplayer content, with both online and local multiplayer having the ability for gaming options with up to four players. However, the game includes a feature that allows the AI to move for you if you don't put your hand on the controlling button; this frees up more time and concentration for precise shots. Because the AI also will tell you which shot is best, you end up with what can only be called "Simon Says," in the words of IGN.
Overall, the only way to describe Mario Tennis Open is "not enough." They started with a great core concept, and at the core it's a great game. Unfortunately, that quality doesn't extend to everything else.