This has not so much to do with coding as such, but there is a great deal of cool architecture involved in this. I'm sure all of you knows about the Xbox game Halo and especially Halo 3 for Xbox 360 from the guys over att Bungie. The single player campaign game itself is wonderful, but once you've played it through maybe you'd like to test your skills against 100.000+ other Halo players on Xbox Live. But be warned, the guys (mostly kids way younger that yourself) are quite skilled, and you will get your butt kicked around.
Everything is tracked
What's so cool about Halo and Xbox Live is that all your progress, matches, achievments, stats, screenshots, film clips and even the latest look of you player model (armour, colors etc) are sent to the Bungie Halo web site so you can track everything from there. You can go back to every game you played and look at details about score, how many opponents you beat down, with what weapon, what medals you earned and so on. You even get heatmaps of where you are most active and successful on each map!
Playing with my son
I'm spending a lot of time at home together with my 12 year old son, who unfortunately got a serious disease in his bone marrow and has to stay at home or at the hospital all the time until he recovers (which will take many months yet), and we're playing a few games on Xbox Live every day - sometimes many games ;) When we've finished playing, we pull up the laptop to look at our player stats on Bungie.net. Needless to say, my son is way better than I am. I'm more used to playing with a keyboard and mouse than with the Xbox controls ;)
These are the Halo 3 stats for my son, and these are my stats. Don't laugh at my stats and rank please...
Interesting game design
I was once into multiplayer game design and development on an open source project for Unreal Fortress *dreamy look* and I sometimes thought about connecting the games to a website in a way similar to what Bungie has done. Multiplayer stats on websites has been around for a long time for games like Quake, Team Fortress, Unreal (and so on), but I've never seen anything like the service on Bungie.net. The game architecture of Halo 3 itself is something too - I'm very impressed with how you can go and look at a complete game afterwards and see EVERYTHING that happened in the game in detail. Not just from your view, but from everyones view. Something I know isn't, or wasn't possible with the Unreal/Unreal2 engine and I don't thing the Quake engine could do that too.
The only thing I miss is being able to change player armour, emblem, colors and such on Bungie.net instead of from Xbox only.
Ranking system from Microsoft Research
Halo 3 uses a ranking system so that every player can earn experience points and be ranked (if you chose to play ranked games) compared to other Xbox Live players. The ranking system is based on Trueskill from the Microsoft Research division. It's somewhat complex but you don't have to care and it seems to work pretty well. If you want to get XP, make sure you end up on the winning team of a team game or in the upper half of a "Lone Wolf" game without teams. The matchmaking system tries to assamble games which are as even as possible, based on the ranks of the players available on-line. Sometimes it takes a minute or two to get a game started, but most of the time it's very quick and many of the team-based games are very, very even.