Some time ago, I became completely addicted to Steam trading cards. But "what are these Steam Trading Cards?" will you ask me, and besides, what is Steam?
Okay, well, I'll make it short and simple: Steam is a video game hub, much like a store (think iTunes or Windows Store, but only for games). Steam works on PC, Mac and Linux, and offers many advantages: to connect with your friends (to play multiplayer), to manage your library of games in the cloud, to be informed about the new games releases and current sales, and many more.
And what are these trading cards? So simply, the vast majority of Steam games are entitled, when you play to them, to a predetermined number of cards related to this game (usually between 3 and 4 cards drawn randomly), and you earn cards while playing (you need usually to play around 2 hours of the game to drop all its available cards), needless to say that when your games library fills up, your number of cards increases in proportion. Then, for each game, the number of cards to complete its full series varies: usually you will need between 5 and 8 cards to complete a series, sometimes 10...
The challenge will be to determine whether it makes sense or not to complete a series. Since each game will entitle you to 3 or 4 cards, while the series always needs more cards to be completed, you will understand that the choice to get all the cards from a series or to get rid of the cards you got will be decisive every time.
The attractiveness of the trading cards system is the Steam trading market. You have to know that the price of a card is on average around 0.10€, it may happen that a 'premium' card (rare) is assigned to you, in this case its market price can sometimes soar up to 2.00€, or more... The question will be then to decide what to do: should I sell my cards? should I try to complete my series? It's up to you to decide according to all the parameters to make the most sensible choice based on your needs, and on the market fluctuation:
It is sometimes an option to sell cards (if possible at best price). As some Steam games are at very low prices (less than 0.50€ sometimes), it's always very pleasant to have some money to afford a game 'for free' or to make a gift to a friend.
Or maybe will you prefer to spare to buy missing cards? Indeed, like on a real stock market, you can post "buy orders": for instance, imagine that you are missing one card to complete your series and that its price for immediate purchase is 0.10€. OK fine, you can post a buy order at 0.08€, and you just have to wait until a seller accepts your price... however, be careful to look at the number of existing orders, if 50 orders at 0.08€ have already been posted, you will be 51th on the list :/ Thus you will have to study all these parameters carefully.
Finally, In addition to the stock market, Steam has an exchange system, again, you are free to share cards with your friends or other Steam users (via the Steam exchange forums).
But what is the purpose to complete a series? Many things: by completing a series of cards, you will "craft" a badge (specific to the game too), this badge will be very rewarding since you will be entitled to some XP points, making your Steam level increase (btw, you can ask yourself what is the purpose of increasing your Steam level? The Game ;) ), plus a nice badge, an emoticon and a wallpaper to decorate your profile related to the game that you completed the series, and finally a coupon discount for another Steam game. Admit that this reward package is quite attractive.
And one final thing to know: each card is actually a full-size 1920x1080px image, so potentially a nice wallpaper for your desktop. Personally, I carefully save every picture from the trading cards I get. But not many users do this, I know I'm obsessive (and it's hard not to become).
In conclusion, you can understand that this Steam Trading Exchange system is completely addictive (And I didn't talk about Gems and Booster Packs...). The quest for XP points being something especially inherent in the life of a gamer, or even if your choice is to sell your cards on the market to fill your wallet and/or make gifts to your friends, you can imagine that all of this can easily become totally exhilarating.