I wish old games could have achievements too, like you said for Halo 2. Like if Bungie went back real quick and added them, then next time we play Halo we can unlock them.
I was a 50 in major clan match, although I haven't played in like half a year and I know that they took away one of the clan games :(. Although the 50 symbol was insane, it's the legendary alien head with dual swords.
For Halo 3 though, every achievement has to be hard. No easy ones- I'll be playing that for years, and I don't want the achievements to all run out. Plus, I hope the max points is booted from 1250 to 1500.
For instance one achievement should be 50,000 kills online which in Halo 2 I definately would have =)