Sounds like it is going to be the new League of Legends. It is funny, a couple of years ago I would have never considered a free to play game because of the difference in quality. Now the quality between this LoL, Firefall (possibly) and DDO it is getting where the free games actually surpass the retail releases on a lot of points.
Personally I'm not in a huge
hurry because I want to finish Mass Effect 2, Nox, Crusader (if I can get the damn controls down) and a couple of Neverwinter modules before it hits open beta (late this year I heard somewhere) or a Guild Wars 2 beta. Whatever comes first will probably be eating up the majority of my time.
I never played much LoL, but if I remember right you could gain advantages through spending money. Characters and such.
If the website for Path of Exile is to believed, you can't pay to get bonuses. You just can pay money to get silly hats or other status symbols.
I could be wrong, but that was my impression.
LoL is more of a 'pay to get what you want quicker'. Everything, minus the cosmetic skins, are unlocked through just playing.
If you want to hit the max level quicker (no real difference except you get matched with better people and get more options for certain things), get the currency to buy stuff from the store faster (ironically these points can also be bought for $ so this one is sort of moot) or just flat out unlock a character you spend $$.
It will never be a competitive game like HoN or DotA but for what the game is you can't do any better. I've spent $30 for the 'boxed' copy that gives you a bunch of crap and I never felt behind the guys who drop $10 every 2 weeks on a new hero (lol),