Halo 3

The halo 3 campaign is probably a highlight of the franchise.
The whole game has been re polished with a new hud and various changes in the mechanics. The controls are even more solid, and the graphics have been touched up for the next generation 360 console.

The main thing about Halo 3 that makes it stand out is the level design and the locations. Throughout the campaign there is never really a dull moment or copy pasted area. You have some homages to Halo 1 levels, such as the level where you start out with a sniper, there are grassland levels full of enemy vehicles are lush beaches, snow levels with dozens of flood enemies in an epic gauntlet battle, and epic sections where you have to board an enemy ship to blow it up. Areas where you enter the flood hive almost turn into horror moments and it gets pretty cool. The driving sections are awesome too, with many huge scopes and sights to see where you'll be flying off cliffs and ramps and doing awesome stunts all the time. Compared to Halo 2, I think the level design is more memorable with less dull moments.

Halo 3 is also pretty short, shorter than 1 and 2 I think. It is also the easiest game on Legendary, as now when you die you can respawn, sometimes instantly, as long as your friend is still alive.

A big gameplay change in Halo 3 compared to 1 or 2, is that no longer do you fight Elites, instead, they are now your ally. In Co op, the second partner is an Elite. it's pretty cool to hear his input and dialogue all the time, and the story and cutscenes in H3 are probably the most interesting and fun to listen to/watch. 
 So since you no longer fight Elites, the difficulty is far easier. As on Legendary, the Elites were the biggest threat in previous games, because of their massive shield which required a plasma pistol to take out.  But now, In halo 3, you are mostly fighting Brutes (which have no shield) or Flood (which also have no shield)  So this makes the combat feel drastically different. Enemies don't feel like bullet sponges anymore, and even on Legendary they go down fast with only a headshot or 2.

Halo 3 being so short could be a flaw, but it might also be why its so solid. The campaign doesn't have a dull moment, and the difficulty on Legendary is just challenging enough to be really fun and engaging, without any of the tedious frustration of Halo 2.

8/10