The main question:
Is it advisable to refuse a job offer in a place you've worked as intern, if you fear it could be uninteresting, poor in terms of career growth, and generally not the best thing you could try?
I'm a (almost graduated) master degree student in Computer Science, currently ending my unpaid internship with company A. So far, while I do enjoy some aspects of the culture of A, I'm not satisfied with the internship; most days I've nothing much to do or I'm forced to wait for input from my overworked colleagues. The project I'm on seemed interesting at first, but now - after months of little feedback and a rather disinterested attitude by, well, anyone - I'm disheartned and I don't care anymore. Of course, I could have been a better employee, but that's a tale for another day.
The point is, now that the internship is ending, everyone seems convinced that I'll receive a job offer soon. This is somewhat dreadful to me, since I'm not enjoying my stay, I'm struggling to care about the project and I don't imagine what my future in the company could be. Moreover, I'm not really conviced I'd like to work with the current technologies I'm using now in company A.
I'll add more meat to the fire and say that, given the actual hiring policy of company A, it's unlikely that I will work there for more than one or two years. As an almost new-grad, I'm well aware there are many things I don't know; I'm afraid of stagnating in a place that won't add anything relevant to my skill set (at least, nothing that I didn't learn through my internship already).