. The online aspect has been opened up to everyone, not just the hardcore players who used Xbox Connect to play Halo online. Unfortunately this also means that you get a bunch of little kids that should not be playing a Mature rated game. Those children are a virus that effects all online console games, Halo 2 isn't alone.
Bungie has done a great job in keeping things updated online. They frequently release patches and have released 9 new maps which are available for purchase now and will be free in August. The servers are relatively steady. Occasionally a game will have a bad host and everything will be laggy, but for the most part it isn't a problem.
The learning curve is pretty gentle at first. The ranking system is moderately effective in pitting players against opponents of comparable skill. Unfortunately the ranking system also means you have people who only care about ranking up and will do anything to do so, so there are plenty of people who don't respect the game or their fellow players.