Some achievements (probably campaign completion, et al) are likely to be the ones that remain the same. But I really liked the thrust of Halo CEA's achievements, where they encouraged alternate styles of play or odd limitations (Leave It Where It Lay, Spare The Little Guys, Speed Reader.) I hope we get more of those. On the multiplayer side since the suite is designed to be integrated I really hope it's just cumulative general playstyle achievements (like "play a match on every map", "win X matches of Halo 2" or something pretty simple and less gimmicky.)