My review of this game will be very different from the majority here since I am totally new to the Halo franchise and fairly new to the shooter genre for that matter, whether it's TPS or FPS. Therefore my opinion isn't influenced by all the other games similar to Halo Reach that may have come before.
First thing: Wow... just... wow...
I wasn't expecting to enjoy it so much but now I truly understand what the hype is about. And being a big sci-fi fan, I think the Halo games are the ones I had always wanted to play, but didn't know it until now. After going through the first mission, I had to literally tear myself away from the game once the cut scene that introduces the second mission ended because I was afraid I might not stop until that mission was over too. :)
One thing which pleasantly surprised me in retrospect is how newbie-friendly Bungie made this game. Even if you've never played a Halo game or any kind of FPS before, you won't feel lost. They completely ease you into it and even though there is no real tutorial to speak of, I never felt overwhelmed during the first few objectives - unlike in a game such as Killzone 2 where you get fed to the wolves right after a very short and lame tutorial. And there are enough checkpoints in Reach not to make dying a very frustrating affair. And again to my own surprise, I only died about 3 times during the first mission.
So even tough I'm really not a great shooter at all, at no point during the game did I feel like my skills were completely inadequate and I think that gave me enough confidence to plough through the battles without constantly searching for cover... and stay there (except when my shield was depleted of course). I have to admit though that I did feel a bit overwhelmed later during the mission but that's because the team was being invaded by a load of Covenant soldiers, including quite a few that were protected by shields. Just remember to always pick up a plasma pistol when that happens... *sigh* Also, this is totally random but I love the Grunts (aliens), they make me laugh. Too bad I have to kill them! :D
Another aspect I loved from this game is the music: it is simply epic and it sets the mood beautifully and perfectly for this action-packed saga. Truly a fantastic scifi game.