Virtual tie between Halo CE, and definitely more enjoyable than Halo 2, 3, and Odst!
The graphic are amazing, and Reach actually has more of the Alien Invasion feeling to it than it did in Halo 2. It's now feels like your in a full scale world war. Some new addition to the Armor is what make this game very enjoyable, like the Jet Pack, and Cloaking feature. Also being able to fight along a squad of Spartans, and UNSC soldier that actually don't die as easily now, makes the shootout feel more intense. And yes, the firefight against the covenant on hard is more insane than any other Halo game in the series.
The only drawback in this game although minor, is some unreal-ism to the game. Like this game is based on the year 2,500, so why the heck are they still using Helicopters like VtoL's that were invented 500 years earlier. It's like using the Wright brothers airplanes from the 1910 to do bombing runs in Iraq today, LOL. And then that level where they go to outerspace. Why are they still using Space Shuttle like technology just to get to space! These things just don't add up to the futuristic time line of this game, and makes the Human look very primitive.
Overall, this is a great game and must have for Halo fans. I'll easily put this at my top 5 favorite 360 game to date. The other's being Fallout 3, Mass Effect 2, Gears of War 2, and GTAIV.