There are terrible F2P games out there with cash shops that dive into your wallet the second you walk in the proverbial door, give crappy service and the food is lousy too once you pick through what's under the breaded coating. You can usually spot those a mile away although admittedly sometimes you can get suckered in by something shiny in your face.
But other F2P (and its close cousin, the Buy To Play) games can be really solid options with a lot to offer. I treat them as super-extended trials - if the game proves worthy of my attention, I give it a "subscription" payment and get myself some bling from the store. If it's unworthy, I'm only out the time and the data transfer against my ISP.
I had a point but I already lost it :P