When I first came to OOP (at first in Java, and then C++) after years of working in C and VB, it was amazing. The idea of extending existing behaviour and operating generically over things of related types was very appealing, and I almost immidiately saw why it was that I wanted this. That is, my motivation for OOP was subtyping polymorphism and inheritance.
Fast forward to today, and I regularly get to use ad-hoc polymorphism solutions (typeclasses and duck typing) which solve the problems subtyping originally appealed to me for in very elegant ways. I have access to parametric polymorphism in most of my environments. Programming generically with these different sorts of polymorphism gives me all the extensabiltiy and re-use inheritance ever did, and more.
So, my question is: why should I still care about OOP? What uses of OOP have you found that are really great besides inheritance and subtyping?
Also, "because it's popular and you will have to use it" does not count. I already am quite familiar with OOP, and use it in my day job because the code base uses it. For a new project, or for myself, that's what I'm asking about.