Pay to Win:
With the Free-to-Play model coming along and developers not making much money off of things like advertising we were bound to see this one. The Pay to Win model is basically the ability to use real world money for in-game items. This sort of gaming model is an utter failure in some scenarios. It divides gamers and gives some players a clear advantage over others. Many games have been able to use the free-to-play model successfully, but some have abused it or have had trouble finding a balance with this kind of business practice.
While some complain about having to still pay a monthly subscription for some MMO titles it may not be an easier way to manage a game and still be fair to every player. Mechwarrior Online game has been struggling to find a balance between folks who are interested in playing their game and willing to spend money on it, from those who are just curious, or have a soft spot for giant fighting robots. The result is an inherent imbalance in the game, where teams are rarely matched up correctly based on not only skill but equipment. This sucks the fun right out of the experience.
