The population has been fine so far for me, haven't had the game long but even last nice at 3:30 AM Eastern time there was still a few servers full. This game really just needs more awareness, I had no idea about it till the other day, wouldn't take too many more people for the player base to be plenty big. If there was 7-8 servers almost full most of the time that would be all it needs.
Finding a game isn't an issue, it's finding a quality game that is my problem. I usually have to play ridiculous games where 16 people are shoved into a tiny map like lockout, or 3 people total on a huge BTB map, and no one wants to stay after the game ends so the player count and team balance will fluctuate for the whole game. Still, I'm grateful that we get a chance to play Halo 2 Online like this never the less.