Crafty - the thing is a kangaroo is a big animal and quite active. Its age, and the part of the carcass where the meat comes from, as well as how it is treated after slaughter, are likely to have drastic effects on what it's like.
If the cow was an exotic animal, and you knew nothing about beef, ad you bought a lump of it from some travelling meat-seller,and just stuck it on the barbie, what are the odds that it would be OK?
Was the cut you had suitable for barbecuing? (Try barbecuing shin of beef and see how well it works). I believe that kangaroo meat is very low in fat, and therefore may not barbeque well anyway.
Was the animal the right age? Beef cattle are (IIRC) slaughtered at 2-3 years old, but naturally bulls can live to 25. An old animal will be tougher than a young one.
Was it hung for long enough?
In short, was it any good in the first place?
I have had it once, a long time ago. I remember that it seemed very similar to beef, but was far too expensive given the quality.