A lot of people dislike Unreal Engine 3 because of how bad it can perform on some computers. Even ROTT is hard to run at max settings and it doesn't look that good.
A finished and polished Dam in Source would look much better than that except for the dynamic shadows and maybe the reflections in the textures.
I know that map is WIP, but like Kraid said, its layout is not good for multiplayer, the scale is a bit big, and it looks low poly like the N64, for example the barriers and tower, there's no point to trying to remake a map and keep those, it's UE3, so it'd be much better to do those with models instead of creating them with brushes.
Unreal Engine 4 on the other hand seems to have great performance and looks even better, but I have no idea how it would be to create mods on it.