My issue with F2P games is the general lack of quality and periodic content updates seen in major subscription based MMOs. The $10-15 per month really does go a long way towards a more enjoyable gaming experience.

Take Guild Wars for example. While it strictly isn't a F2P game, it is a better quality MMO that doesn't require monthly payments. And without monthly payments, the amount of content is pretty lacking. I own all the expansions for it, but after clearing everything with no new content on the horizon (save for infuriating skill changes), it's hard to continue playing.

Conversely, WoW is where I can always expect new content and activities in between expansions. I just don't play it now because it eats up time :(

So indeed, MMOs also follow the "You get what you pay for" proverb.