The worst thing about it is they pick the women for you.* They'll send you a few each day. You can't browse around. I did not email ONE woman from the "matches" they sent me. The women there are looking to get married. No ifs ands or buts.... they want to get married! If that's your game, it may be good for you. I'm divorced and NOT looking to get married again. Unless a gun-toting supermodel comes along and insists I don't sign a pre-nup....
Match.com has given me the best results. I've had two semi-long term relationships (over a year) with women I met on Match. I've also been on plenty of "one time" dates that went nowhere. I guess I'm weird as I don't mind dating. I actually enjoy meeting new women, even if it doesn't work out. And I always pick a decent place to eat. So at the very least, I get a good meal.
Plentyoffish.com is a large free dating site. My general finding is the women are of lesser quality than those on Match.com.
I really should write a man's guide to online dating

*This was a few years ago. Things may have changed.