Most everyone is familiar with tic-tac-toe and its more evolved cousin Connect Four. Gobblet (and StackEm, which uses almost exactly the same rules) shares the goal of trying to make a line of your pieces across the board – in this case, four pieces either horizontally, vertically or diagonally between the corners – but adds in the important rule that some pieces can gobble up (i.e., cover) other pieces.
Each player is given a set of 12 pieces, three sets of four that nest inside one another. Thus, there are tiny, small, medium, and large pieces. In Gobblet, these are simple wood cups, and the game has an elegant look. At the start of the game, each player has three stacks of pieces, and you can't play a smaller piece until you've placed a larger one to uncover the smaller pieces underneath in your deployment area. Once on the board, everything but the largest pieces can be covered by any larger piece (yes, you can cover your own pawn, perhaps to reveal it later as a surprise). Multiple pieces can nest inside each other, as long as each one fits. If the game goes on long enough, it's easy to lose track of which pieces are where.
Other than that, Gobblet/StackEm is your standard two-player abstract game. You take turns moving and deploying your pieces until someone achieves the winning condition. You don't need to get everyone out on the board before moving pieces around, so there are a lot of options to choose from each turn. Basically, if you are allowed to put a piece onto a space, you can take it from anywhere to do so. It's not chess, but it is a solid way to wait for your food to arrive at the diner.
We'll start with what's good about StackEm. First and foremost, it's got a gorgeous, clean interface that never makes you wonder what's going on. The design is clear and you can easily tell the pieces apart because of their size and different grimacing faces. While they are kind of cute, I'd be a great option to have the same simple, wooden pieces that match the look of the tabletop game.
Other good features of StackEm include OpenFeint integration with leaderboards (although exactly how the scores are calculated are unclear) and that two players can play locally using Bluetooth. Grimes told TUAW he's planning on incorporating Game Center multiplayer into the app shortly after iOS 4.1 is released. He said the Game Center reset "has put a hold on all my testing for the moment. As soon as we can test again and I can shake out any bugs, I'll be submitting v2.0 for approval."
One difference in StackEm from the Gobblet rules (as published here [PDF] by the producers of the tabletop version) is that you can place a new piece from off the board onto another piece even if that piece is not threatening to make a line of four right away. In StackEm, you are allowed to pull a new piece onto the board to any space, as long as it's empty or has a smaller piece in it.
A more important change is that StackEm doesn't give players the option to look under their pieces to see what's underneath. True, the official rules don't let you do this either – if you touch a piece, you have to move it – but you can play a friendlier game with the tabletop pieces (against your child, for example) if you remove the harsh memorization factor. As it stands, don't try to lift a piece to peek at whatever is underneath in StackEm, as that will count as a move. In fact, don't tap the board at all until you're sure of your move.
Graphically, there's not much here. StackEm is a simple, colorful affair with three different board colors (look through the gallery of screen shots to see them). You cannot adjust settings in the middle of a game except by exiting the app and restarting (the app does save the gamestate upon exit). The problem is, if you do this, you can sometimes muck up the game colors (see the example above) which makes the game kind of trippy. I recommend just restarting the game with the settings you like if you need to adjust something. Also, you can't play the game horizontally. It's portrait mode or nothing, even though you would think having the faces rotate to always be right side up wouldn't be all that difficult.
Now we get to the bad stuff. First, there is an incredibly annoying "You win!" voice (and some cheering) when you beat the computer that can't be turned off. In fact, none of the game's sound effects can be disabled (without, of course, cranking down the system volume of your iPad). You can play iTunes music with the game on, but the rattles and other sounds will play over whatever you're listening to. Second, and most importantly, even on the hardest setting, the AI makes some really dumb mistakes. The biggest? Not blocking me when I had three tiles lined up to win. That's kind of a big deal and shows that multiplayer is the way to go with StackEm. Hopefully, future updates will beef up the computer opponent to a level that doesn't miss obvious plays.
Interested in trying out Gobblet online before buying the app? You can do just that here.