I believe nothing at all about playing video games is "hard core". Calling someone a "hard core" gamer is practically an insult. I love playing video games, but jeezus, stop trying to make it sound super cool or something.
CE: 5 Stars - Gameplay was fluid and fun to play on a console, and the multiplayer design made it a game I played with friends for years.
2: 4 stars - I didn't hate the capaign as much as other did, although Arbiter levels never interested me much. The online multiplayer, however, set the console standard until COD 4.
3: 4 stars - A much more polished capaign than 2's with a servicable ending, however the graphics were a bit of a letdown. Multiplayer was a solid and mostly predictable expansion on 2, but by then I was pretty much done with it.
Haven't yet played ODST or Halo Wars.
In total, Halo is a great series that never really lost it's footing. It's style of FPS gameplay kind of lost the crown when COD 4 took over, so unless new games take it in an incredible new direction, I think it's time is mostly over.