I like the system, but I'm an overachiever with loads of time on my hands so it's no wonder why. Also, it gives me more of an incentive to play a certain game, such as Portal Defenders. As for the idea being a copy of Xbox? I believe Xbox by itself also copies achievement systems from other games and such. It's a trend that's been spreading like crazy so unfortunately it's really hard to point two fingers and say "you stole this from that!" I believe that the people here at Newgrounds have a lot more in mind with this system and that they'll probably show up with something sweet :) I as well look forward to using it with a game someday, if I ever get one finished.
I give it a 10/10 :]
Oh, and the bragging rights are nice, too.
Trak888
Kongregate online games has the same thing but for far more games, and they also intend to add downloadable prizes, the more points you earn through playing the more stuff you get.
funorb also has the same system.
Newgrounds is kinda lagging behind and some of the games they've given medals to are annoying. Sometimes i'm not even awarded medals!