I enjoyed the new map...infact it has gotten me back into Halo 3.
As for the Valhalla/Blood Gulch thing, the problem with that map is the middle high ground.
Capturing this provides you with the high ground and hence an advantage, this causes people to go and capture the middle ground. Because of this the fighting takes place between the hill and the base which halves the size of the map, or at least the areas in which people play.
By having the rocks and cliffs around the map this stops vehicle combat. The two missile pods and Spartan Laser keep the people out of the vehicles as well, the man cannon allows for people to move to the middle of the hill far too quickly which means you can just spam players into the centre of the map until you take the most strategic point and then you camp there while the enemy spams players at you. The only good game type for Valhalla is King of the Hill with a single point in the centre.
Blood Gulch does not have this strategic point and is much more open. This focuses the fighting between the bases and thins length encourages the use of vehicles, nay enforces the use of vehicles. The single Missile Launcher in the middle of the map also means that vehicles must face vehicles, this in my opinion makes objective game types much better.
Valhalla is not Blood Gulch and no amount of forging will change that, thats why we needed a map like Blood Gulch for Halo 3.
Sorry for going a bit off-topic but people saying the two maps are the same don't know what they are talking about.