It's good for your first map! More an artwork and intended to learn mapping, am I right?

First of all, you should have a look at the packaging guidelines: http://www.quadropolis.us/node/226
... and use lowercase for all file names :)

To the map: Like I said, it's quite detailed already. In the house you could build some different kinds of pools, a large one to swim in and a smaller one for ogro-kids :D
Or add stairs to get out of the water.

The lighting is quite empty yet. Try to create lightsources and set in more lights to make the interior design of the poolhouse more interesting :)

i like its simplicity and the sewer is cool. all i would do is add a hole in the ceiling so you can get some light in there and another thing i would do is add somewhere for the water to run further down the sewer.