I have it. GREAT lens. However, being a macro, I've noticed it has a narrow focus angle, so top-down shots will be relatively small and close-up at what I'm assuming are your range limitations. I wouldn't go to it for deep shots. I'd go to a small telephoto.
Edit - do you own it, or are you considering buying it? I can take a few shots of my own tank if you'd like me to, for a demo.
Certainly an excellent, excellent addition to your lens collection. My 100mm is easily my favorite lens. If you look up the "Melancholy" picture thread here, my entry was done using it.
I also shot an old worn-down silo that was kind of neat, but this one is a little more morose. Working in south Chicago and living in NW Indiana, subject matter was not hard to find.
Comments/ critiques are welcome. I've had this camera for less than a month but it's immense fun learning it.
Just noticed I'm using it in my avatar!