A finalist for the Spiel des Jahres award in 1999, Uwe Rosenberg's Mamma Mia! is not as well known, or arguably as deep, as his game Bohnanza, but it's a good game for a party setting, accessible enough for kids and yet with just enough strategy to hold the interest of sterner gamers.
From a game design perspective, it's interesting because there are essentially three layers to the game.
Each player has a set of 8 pizza cards, differentiated from the other players' cards by the color printed on the back, and by one ingredient -- e.g., the green player's pizzas all require at least one pepper, the brown player's pizzas at least one mushroom, and so on. Except for this point of differentiation, the sets are identical. Before play, you take your set, shuffle it, draw one, and leave the others face down near you. Your ultimate objective is to "fill" all these pizza orders; at game end, the player with the fewest unfilled orders wins.
In addition, there are a bunch of ingredient cards, which in a non-pizza themed game you might call suits: mushrooms, peppers, pepperoni, olives, and pineapple. Each player is initially dealt six ingredients at random.
During your turn, you must play at least one ingredient card from your hand, and may play any number, as long as they are all the same kind of ingredient. You may optionally play a pizza card from your hand as well. Then, you replenish back up to 7 cards, either from your pizza cards, or from the ingredient deck.
When all ingredients are depleted, you turn the cards people have played over, and turn them over one by one. Ingredients are sorted into piles by type. When a pizza card occurs, if the ingredients required to make this pizza exist in the ingredient piles, it is filled, and removed from play. If not, and the player who played this order has in his hand the missing ingredients, he may play them from his hand to fill the order. And if that doesn't work either, the pizza card is returned to the player's stack of pizza cards, unfilled.
Then, ingredients used to fill pizza orders are reshuffled, placed face down, and a second round begins. The game ends after three rounds.
From a naive player's point of view, this is a fun, somewhat random card game with an entertaining theme, and one that certainly anyone over 10 can play (and possibly brighter younger players). From a serious gamer's perspective, it's essentially a card counting game; you try to keep track of what ingredients have been played, and judge when it's safe to play one of your pizza cards on the basis that sufficient ingredients exist in the pile to play it safely. Or rather, you may not want to wait until then, because other players may be more aggressive and screw you up by playing a pizza before you do -- so you may want to make sure to retain in your hand the extra ingredients needed.
What prevents the game from being purely a function of card counting, however, is the fact that each player's set of pizzas contains three somewhat unpredictable cards. One card (Pizza Bombastica) requires 15 or more ingredients, and clears out all ingredients currently in piles, very likely screwing the player of the next pizza in the pile. Another (Pizza Monotoni) requires exactly 6 of any ingredient (plus one of the player's characteristic ingredient): if multiple ingredient piles have 6 or more, the player who played the pizza chooses which is used. And the third (Pizza Minimale), uses exactly 3 of the ingredient that has the fewest cards in the piles -- with the pizza's player choosing if tied.
Thus, even if you're perfect at tracking what cards are available for the next pizza, you can still be screwed up by these cards, and by the unpredictable choices of the people who play them -- who may well make those choices with a view to screwing up the other players.
These are the three layers of the design: simple card play; card counting; a scheme to ensure that the game does not degenerate into simple card-counting. You can almost see Rosenberg's thought-processes at work here. Which I, at least, find interesting.