There are two different kinds of halo fans... There are Multiplayer fans and there are Storyline fans IMO... Halo storyline fans play the games because of the story, they play to enjoy the roles they are given, to discover things they never knew about the story (from terminals and such). Being a Halo Multiplayer fan is different entirely, playing the game for the sake of playing a good FPS.
The AA's IMO were a neat addition, making you have to think more about who has what ability and how they are going to use it and plan against that ability.. The use of armor lock and invisibility are not bad things, they are useful for different game modes, you would complain if you were playing in say, an invasion match and trying to snipe but you couldnt because everyone could see you and would shoot at you any time you tried to shoot at them then maybe you would think "Hmm if only I couldn't be seen for short periods of time"..
Anyways.. I agree with Mystic here.. Reach is a Halo game same with Halo wars and ODST, they just develop the overal story of the Halo universe more thoroughly, like, if I remember correctly Halo Wars started off on Harvest..? which is where the war started... And ODST was showing what was occuring in.. I always forget the names of the cities, was it New Mombasa? during the course of Halo.. 2? havent played 2 or 3 for a while so I forget which one had the supercarrier jump in orbit...