Just a hard drive error probably. Just insert another the game then put Reach back in. Also most of the players who asked me this confirms they quit while it was loading or saving. There is a reason why they ask you not to.
Reach is just different game style. Its not bad a game if judge unbiased but to the audience halo usually targets it isn't good becuase the people likes Halo 3 or Halo 2's style.