You should probably avoid putting secrets as it did take the fun out of your other map. The only kind of tolerable secret would be an Easter egg, like a sticky note on lost temple or a custom song that plays through a radio.
And also, you should avoid placing a large skybox around your map as this leads to optimization issues. Then when your map is ready for release, compile it under HDR Full Compile Final -slow!, in the Expert Compile Dialog Box, as this will dice/cut your visleafs thoroughly and will prevent artifacting of ambient light coming from the skybox. Obviously, this will take about x3 longer to compile but it will be worth the wait.
Other than that, I'd say I can't wait until you finish this as I always see you like to utilize as many props from the HL2 universe as possible.
