With the number of quality free-to-play 
online games growing almost daily, dropping $10-$15 per month in subscription fees is getting harder and harder to justify.
Walking away from a free online game, after all, is a pretty easy thing to do. There’s no nagging voice in the back of your head doing the math and informing you of how much money you’ve invested in a game you’re no longer obsessed with. When it’s free, the stakes are low, though often so is the payoff.
Chris Morris: Journalist 
I suspect that if you get right into a Free-to-play game, you’re likely to spend more on it than a monthly subscription based one. New character slots or options, new adventure packs, needing more inventory slots etc, and over a year the free game ends up costing a surprising amount.