Looks pretty good actually, but can still receive some enhancements. I really like the general layout of it, with pretty long ways but also so much challenging that makes it pretty difficult at many times, specially in that part that you mentioned which is about minutes of unending surfing.
Texturing is decent, I like how detailed they are, and also how attractive they do look. However, I have to agree with Nitekillr, you used one texture everywhere, it is always the same for the ramps, the glasses and the background, and taking into account that those are the great majority of things that are on the map, it becomes annoying after playing it plenty of times, what you should do is to make some variations by using other textures that have a similar looking, for example placing ones with different types of rocks with different tone and different aspect/shape to at least make some of the areas look different with each other, on another note, the glass texture you used is a bit undetailed too.
I don't really hate that brown color running all over the map, it's just it's repetitiveness what bothers me; every area has the same theme, with no notable changes with respect to others that makes me think that I'm going in circles. In other terms the texture still improves the map's construction and gives it a good ambience for a surfing map, although I would suggest trying to apply the suggestion I left before. Ending the jail is also plainly gray which makes it loss appeal, and even the the sun effect can't help to make it look alive.
The designing is quite special, it has plenty of extras and fun but also lots and lots of creativity: More than twenty secrets! Ramps do look pretty well done and don't look squared, I also love how do you make big windows to make the skybox viewable through them, that is a really nice improvement for the map's visuals and looks really refined.
Although the creation in some areas makes the difficulty go from beginner to expert, just compare the first parts to the descendant area where there are about three heavy 180 degrees turns and where is very easy to lose, makes it get somewhat unbalanced. Aside from this the overall structure needs a lot of smoothing, it is just enough with looking to the deep corners where the walls turn to the roof, also environments that are meant to be curved are lacking smoothness too.

I have also found a bug with your water surfaces at the jail, it seems that if I go back looking to one of them, and then return again it will reflect the world improperly:


On the illumitation, looks pretty good because of the sunlight environment you added, nice use you made of that option, it looks delightful and I loved it when I saw the ramp that is between the spawns!
Although I encountered with various light sources that are actually coming out of nowhere:


The reason why the parts that are in the deeps of the map aren't dark, is because of them:

It is actually pretty good, although there could be minor bugs.
The single-player gameplay (I didn't play online, and bots can't do anything on the level) is pretty challenging and nice as I said earlier. I love how you adapted some of the areas for beginner use while you made another paths for expert surfers, also I like how you made gameplay not look same-sounding in every place (by design), besides that in the lowest point on the map there are many glass floors that are fun to pass through the area by them. Aside from that you included most (Or all, I'm not sure) of the weapons, which is a feature to enjoy, gameplay is just beautiful at least when playing alone for me.
Overall, I can't rate, but I would give it a 9.40 in my opinion, there are only issues in the design, like the non-smoothed curves (At exception of the ramps) and the repetitive texturing. However my rating will still stand because of the awesome environments like the evn_sun and the awesome and detailed skybox. Also a little help to fix the curves would be this tutorial, I recommend following it.
Your map is one of the bests of all time I have seen, keep it up!
This needs little to no improvement!
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