Simply put, the game is great out of the box (free). I haven't paid a cent yet. Those who have paid can get access to other classes that have different weapon loadouts, but overall I'm dying to newcomers as well as veterans. It's how you use those loadouts that count. Experience gained will eventually give you breathing room - for a while. Just like any other game, there's always someone who'll be able to kick your ass now and again.
As far as paying goes, I'm happy I don't have to. However, I also would have bought this game had it not come out as free to play. Given that line of reasoning, I personally wouldn't spend anything over $50 - if and when I decide to open my wallet.