The package is large and takes a bit to import. It is extremely detailed, and there is so much to it that I can tell the author loved building this.
Here's some tips when you get it imported:
You'll want to drop in a FPS controller (use the rigid body controller in standard assets so you get a collider to open the doors) to explore the school. It's dark inside (but super cool atmosphere), so drop the added flashlight prefab on the FPS controller so you can see your way around.
Download the post-processing stack from Unity and import. Set your FPS camera to use Deferred rendering, add a post processing behavior script to it and assign the preset profile that comes with the pack. Next, assign the "MainCamera" tag to your FPSController (the parent, not the camera because you'll need the collider to trigger opening doors with the "E" button).
Next, go to Edit > Project Settings > Player and set the color space to Linear.
That should get you going to play the demo scenes (there is a day and night scene already lighted pretty good). Note that if you are using the FPS controller from Unity, there is a bunch of items that block the hallway to go to the gymnasium that you'll want to hide so you can walk through. The gymnasium is SWEET.
Now for my general impression. This asset kicks butt. I opened up an empty scene and started dropping the modular prefabs into it and was building my own school (heck, it doesn't even have to be a school, it could be an old insane asylum or whatever!) and snapping it together in no time.
I can see building a HUGE building out of this. I'm thinking of creating a building for the entrance of a prison where the warden's offices are (if you've ever seen Shawshank Redemption, the building style reminds me of just that).
I really hope this author makes more like this. I have spent easily $2000 on building environment assets over the last year, and this asset is my personal favorite. Brilliantly designed, and with the custom surfacing you can do on select objects, you can easily create AAA scenes that will blow people away.