if you're lookin for a great shooter, get it. if you're lookin for a deep storyline to go along with it...
Let me just start off by saying that Halo: Reach is an absolutely amazing fps. Bungie went all out with the gameplay in their last installment of the Halo series. Marty O'Donnel's score is better than ever. Enemies are clever and diverse, graphics are beautiful, maps are twice as awe-inspiring as they were in Halo: CE, armaments range far and wide, etc. Online play is where the game really shines. Customization has improved significantly. Forge essentially has the means to keep multiplayer alive for years to come. The best of ODST (Firefight) has also been brought in, along with the awesome classic multiplayer that has made the series so popular.
But the single player storyline - a factor that I have kept close to my heart since the first Halo installment - left me disappointed. That's something that really broke my heart. I won't let loose any spoilers, but with past Halo games, stories were largely character driven, and always ended on a high note. While Halo: Reach has the perfect setting and the gameplay elements to pull off that sense of "epic-ness," it just fails to hit that high note. And it's not just the ending. It's a variety of aspects. Characters are, in my opinion, woefully underdeveloped, and I can't help but notice the lack of impact whenever the story takes a twist.
Aside from that, Halo: Reach is still one hell of a game for Halo fans and fps lovers alike.