[rdhatt]

"Opinionated" means the software has made very deliberate design tradeoffs and is very inflexible/resistant to changing that. This is done to optimize certain objectives like software scope or increasing productivity by enforcing certain methods.

So in this case they cited "no client-side routing wiz-bang" -- that's one of their opinions and won't be introducing any support for that sort of thing.

The classic example is Python's motto "There's Only One Way To Do It", which was in a response to Perl's "There's more than one way to do it."

Another example is Ruby On Rails...it has a strong opinion on how the application should be structured -- must be MVC, most of your code should be in a model, convention over configuration, etc.