Free2Play games have been plagued with a ton of problems, with most of it involving a solution to revenues on a free game. Here's a list of different reasons why I don't play a lot of F2P anymore, and most of them involve MONEY.
1. Cash shop imbalances - Let's see... Combat Arms, Wolfteam, Perfect World, Flyff. These four games are notorious for making you buy the best gear in the game with real-money currency. Sure, on an FPS game if you are good enough, that means you can just use a mediocre gun and be good. BUT, what if someone who could do the same uses these cash shop weapons that no regular ingame shop weapons could match? There's always been this stupid idea the developers use to make revenue. Alliance of Valiant Arms still allows you to buy weapons with Gcoin, but aside from the novelty capsule weapons, you are able to actually buy them with ingame Euros and the appropriate rank (whereas Gcoin weapons are usable at Rank 1). Of course, the downside to that is you cannot sell GCoin weapons (not that you want to anyways, since 10% is a fairly low return).
2. Cheating - This is the biggest issue in F2P games. There's either a blatant hacker, or people ingame are creating paranoia of said hacking. This makes every other noob and their mother scream HAX like they were about to throw their monitors at someone, whenever a good player rolls their face with the most mediocre weapon. Also, the anti-cheat systems on these Korean-based games are below subpar. No, really. In Korea, it's a felony to hack even in a video game. You will get some jail time plus you are banned from PCbangs (LAN Centers), especially because your account requires a KSSN. In Japan, it's just part of their culture to play as fair as possible.
3. Gameplay - Games like Vindictus have amazing graphics, but the gameplay is bland and repetitive, and with only 3 characters to choose from, it's very stale. Then there are games like AVA that have great weapon balancing for the most part, but is plagued by item #2. Upcoming games like APB try to limit your weapons and customization levels in an attempt to fish some money out of you. Many more are just poor clones of each other. Some even go to a point of almost mimicking a game. 4Story (Gates of Andaron) and Runes of Magic are total clones of World of Warcraft in terms of the UI and some gameplay mechanics.
Seriously, I think one of the few games that try their best NOT to jump into these mistakes is League of Legends. Runes make your champs more powerful early game and sometimes mid game, and you can only buy them with IP. Of course, you can buy IP boosts, but it's totally optional. I have 3 complete runebooks and it only took a couple of weeks of playing about 2-4 matches average a day. Champs are buyable through IP or RP. Skins are there for vanity, and some people like them enough to purchase one or two. Alliance of Valiant Arms comes in a close second, but they sort of break item #1 with the FG42 and Sidewinder and item #3 with the SPAS-15.