Bohnanza is a trading game with a bean-planting metaphor (the title is a pun in German, its original language of publication: bohn means "bean"). As with most Eurogames, the metaphor is largely irrelevant -- and in some ways detracts, I think, from the game; the theme and imagery make it seem like a children's game, while in truth it's a game of serious strategy.
The card deck contains eleven different kinds of beans, with a varying number of beans of each type. The basic idea is that you want to "plant" (play in front of you) as many beans of a particular type as possible, because you earn more "coins" (victory points) the more you plant, in a less-than-exponential but more-than-linear way. However, you are constrained by the number of different types of beans you can have planted at once (two, or three if you spend coins to purchase a third bean field), and at times, you're forced to play cards, which may require you to "sell" a planted field, for whatever value it provides at the moment.
Each player receives 5 cards at start, and may not reorder them. During your turn, you must play the top card in your deck, and may optionally play the second. This, of course, may require you to sell one of your bean fields. Then, the top two cards of the draw deck are turned over; you can trade these with other players, or donate them to players who will accept them, or plant them yourself -- and if you cannot make a deal to get rid of them, you will again be required to plant them. Any traded (or donated) cards must be planted at the end of the phase, by your and your trading partners, after which you draw three cards and place them at the bottom of your own deck.
The strategy is, of course, to maximize the number of cards planted in each bean field before sale, but doing so is tricky -- and trading is key, since it's the only way you can get beans out of your hand before you're required to play them. Keeping track of what other beans the players are accumulating is important, too, particularly for the rare but high-value bean types. Card-counting can be helpful, too -- when bean fields are sold, some of the bean cards are flipped over (each has a coin on the back), and the seller keeps as many, in the forms of coins, as the value of the sale; the others are discarded, and shuffled back into the draw pile when it is exhausted. You go through the draw pile three times during play, so the number of beans available of each type diminishes over time.
Thus, while the luck of the draw has a role in Bohnanza, and prevents it from being as dry as more abstract strategy games, Bohnanza is mainly about strategic thinking, and negotiation. It's also fairly inexpensive, and playable in a half hour -- a fine game for a party or "game night" setting.