Many years ago, I got the first Xbox during the holiday season it was released. Most of the games were terrible but there was one that stood head and shoulders above the rest--and revolutionized the first-person shooter genre for me and many of my generation. That game, of course, was Halo, which I probably played for more than 400 hours, reliving the campaign over five times on various difficulties, and playing many missions dozens more times (along with the game's great multiplayer) with my friends.
Halo introduced so many features that are now the default/baseline for first-person shooters, it is almost fair to say that it invented a genre (the modern console shooter) as we know it (for instance, imagine how many shooters you've played in the last 5 years without rechargeable health or shields--a Halo staple).
With that being said, it's hard for me to approach Reach objectively. Rather than standing on its own merits, the game will always, for better or worse, stand on the shoulders of giants--and be judged by their quality.
In general, I think Halo Reach succeeds admirably. It provides a tight, entertaining campaign of near-perfect length, and with a storyline and production values that stand above the rest of the fields in its most dramatic moments.
Which is not to say that the game is perfect. I just finished it about 30 minutes ago, and on reflection there are two clear criticisms that stand out in my mind:
First, the gameplay has not evolved much (if at all) since the first Halo, and neither (to a substantial degree) has the level design, at least from Halo 2 or 3. Outside of the lone space mission, which was pretty intriguing if not fully developed (it's no Rogue Squadron), you're pretty much going to be doing the same stuff you've been doing for 10 years now--clearing corridors and rooms on your way to a pretty arbitrary objective, that typically is completed just with the push of a button (activate this, deactivate that, etc.).
Second, there is a slight balance issue with the weapons. They feel just a hair underpowered. It's a bit frustrating to unload half a clip into a grunt before they die. Those guys are peons! It undercuts some of the "elite super-soldier with powered armor" aspect of the game.