Yass! I've been there twice- really good! Yeah it's small enough but really authentic and enjoyable- amazing views of Edinburgh and cheaper than touring those places on a sightseeing bus!
Personally, I found it worthwhile for the money. I ended up spending a good few hours wandering around looking at everything. Although it's a fairly small site, there were actually quite a few different bits and exhibits to see there. They also have guided tours included in the entrance fee if you want to do one (or at least they did when I was there a few years ago), which I found quite interesting. Having said that, I'm quite into my history so for me it was one of the must do things in Edinburgh. If it isn't your thing, I wouldn't spend £16 or waste time there that you could be doing something you'd enjoy more