Sorry you felt that way.
Yes it might not a place to see many birds or insects, but you can see rare animals if you are lucky and if they are treating some at the hospital.http://www.lakdasun.org/forum/index.php?topic=129.0
It is not a zoo but a conservation center ne, where they treat and release as soon as possible.
So they may have few animals or a lot depending on your luck.
And we must remember that this a center where all the work is done by volunteers.
They are not supposed to be guides, although they will kindly oblige if they don't have urgent research work or work at the hospital etc.
The fact is they have ongoing very important research like the Primates research in Sinaharaja.
It is always better to call and go I think.
Hope you will have better luck next time!