Some friends of mine love Runes of Magic. Basically WoW but free. I've tried both and they seemed the same to me, but I'm not big on the hack/slash stuff and didn't play long.
I played Runes of Magic for a few months last year, without spending any (real) money. Had a good time, got to the level 50 cap (it's gone up since then) without getting the feeling of being too badly disadvantaged against the players who did buy in-game items. Okay, my class choices were not very equipment dependent which made a difference.
Eventually you will have to stump up some cash or you will get left behind your peers, and that can get expensive. That for me was the time to quit, but I did get those months of fun gaming for nothing.