Call of Duty: yearly installments, minimal changes to gameplay, BO2 had 2 years development.
Halo: 2 year installments, whole new enemies, game modes, weapons, actually good stories, 4 year development cycle for this one IIRC (I believe 343 Industries began working on this the same time Bungie started working on Reach) --- Pro Tip: don't put anime spoilers in your sig. I got suspended for it.
This game is going to be awesome. Get it. I haven't enjoyed a COD campaign since 3 so that leaves the online which will probably be exactly the same as always. --- "You can lead a whore to water and you can bet she'll drink and follow orders" http://www.last.fm/user/GloryisdeadX