Halo was like the biggest game for me at the begining of this century. I didn't ever get into multiplayer, but I loved co-op play. For the me the series only got better until the crowning achievement of Reach. Halo 4 has some changes that bothered me and made it a little less fun, but I still follow the series in all its forms: games, books, comics, and I guess a TV show coming soon from Spielberg.
I don't get the bashing. I'm not particularly interested in COD (the modern warfare ones) or Battlefield games, but I don't have anything bad to say about them. They're good for what they are. I may even try them someday. But I'm a Halo guy. I like my scifi and my amped up super soldiers and Halo does that better than anyone.