It is a dangerous thing when, in the course of engineering,
you have a solution looking for a problem, instead of a problem
looking for a solution.
I'd say that the biggest benefit in using IS-IS over OSPF is
the tuning of route metrics, but aside from that, I'd say that
the two routing protocols are substantially similar enough to
warrant close consideration of exactly what one would want bad
enough to switch from one to the other.
- ferg