I don't want to come off as a jerk, but this post is going to be very critical, and hopefully you'll be able to take it constructively and be able to use it to improve your maps in the future:
First, the title: If you're going to call it Valhalla, just call it valhalla. I don't see how that's associated with cP in any way. Just because you're in a clan doesn't mean you have to name a map after it.
Next, performance: This map pretty much combines all of things that cause poor performance in Paintball2: Large, open areas (since bsp chops them up), no real visibility blockers, water, poor brush alignment (gaps/unsealed areas all over), and tons of entities. The r_speeds are in the red pretty much everywhere, and you really need to avoid that. You can't expect everybody to have a high end gaming machine. Most of the people who do aren't playing this game. Even my machine, which plays BF3 fine, drops down to like 30fps sometimes.
Latency: All the entities you've added for grass, trees, etc. actually add networked entities which take up bandwidth. Also, since the map is basically just a big box with no visibility blockers, all entities (players, paintballs, etc.) are going to be sent over the network all the time (in addition to all the trees and such), likely resulting in overflows or just a laggy experience overall.
Visuals: I'm going to be honest, the map itself doesn't look very good. It just looks like a bunch of giant wedges haphazardly placed around. I realize it's a work in progress, but I think you're going about it the wrong way. The base world terrain should all be aligned. Snap your verts to the grid and such. Also, having the water exactly at the height of the trough, or whatever you want to call it looks weird, as does the fact that there's a waterfall flowing into it from each side. Where does the water go?
Gameplay: The map is almost symmetrical, but not quite. There are some pretty significant differences in the terrain that will probably make it easier to take a shortcut to the flag capture point on one team. The jump pads are kind of an interesting idea, but I think they mostly provide a crutch for the fact that the map is super large and you're going to be spending most of your time traversing terrain. There isn't very good flow to the map. You take a jump pad and try to move across the terrain and slam into a giant block rock that's jutting out of the side or a tree or something. The bases seem mostly pointless. I can't see any reason to go in the lower area, and it makes the ramp up to the capture point awkward. Overall, I imagine the gameplay just boiling down to finding the perfect path where you can move along without hitting trees or rocks, and just speed capping over and over.
Suggestions to improve it:
I think your best bet is to start over and rearchitect the map so it has better terrain and visibility blocking. I would make it more of an S-shape. Try to make it so you can't see more than 1/3 of the map at a time. I would also cut down the map size quite a bit to make it faster to navigate without the uber jump pads. The number of visible trees should be cut down to like 2 or 3 at most (and try to put them in locations where they'd provide tactical cover and not block movement). I'm not sure what to suggest on the bases having not played the Halo version of the map. They certainly need more visual detail and practical playable space, though.
