A few comments regarding Nagarjuna:
First, Theravada does not need Nagarjuna. I would argue that no one does, meaning that no Buddhist tradition needs his analyses in order to practice, follow the path, attain realization. In other words, I don't think Nagarjuna is particularly insightful nor do I think his writings particularly relevant to how the vast majority of practitioners engage the Dhamma and Dharma.
Nagarjuna is obsessed with articulating a finely wrought analysis; but how does that help one's practice? How does that help one achieve realization? I think it is all colosally irrelevant.
Here's an analogy as to why I think this way: Cultivation does not require perfect understanding of ultimate nature. If two gardeners have different understanding about the ultimate nature of "flower", those different understanding will not impinge on their abilities to garden effectively. Both can still produce wonderful gardens.
Similarly, understanding precisely and meticulously the exact nature of emptiness does not, in and of itself, prove conducive to effective practice of the Dhamma Path. It isn't needed in order to practice the precepts, enter into the foundations of mindfulness, or practice metta. Whether one comprehends emptiness as a non-affirming negation, or an affirming negation, or as a mystical darkness, all of these are equally compatible with Dhamma practice.
On the level of logic, I remain unconvinced by many of Nagarjuna's arguments, particularly those that rely on equating an infinite regress with a logical error (see, for example, his analysis of motion). Not all infinite regresses are fallacies; one has to further establish that the regress is logically vicious and Nagarjuna does not do that which, in my opinion, vitiates many of analyses. In addition, Nagarjuna often wins his arguments by defining his terms in an eccentric way; the link that Tilt gives offers one example of this. 'Self-nature' as used in Abhidhamma/dharma does not necessarily entail separate existence, which is how Nagarjuna treats it. Just as an ecological analysis of a field does not entail the separate existence of the elements of that field (the science of ecology would actually deny that conclusion), so also the listing of mental dhammas does not entail that they have separate existence. Nagarjuna uses a sleight of hand here to win an argument, but his victory had almost no influence on his opponents because he wasn't really addressing their claims.
I have a deep admiration for thinkers like Proclus, Spinoza, and Nagarjuna who are able to manifest a finely wroght analytical structure. There is something beautiful, to my mind, about these offerings, but they are not the final say on Dhamma. One philosopher I greatly admire, Alfred North Whitehead, says in his preface to "Process and Reality" that there is no such things as a final system of analysis. Creating a final system is not really the function of these kinds of analyses.
One of the things which disturbs me about the focus on Nagarjuna is that Mahayana Buddhism seems completely stuck in this medieval system and logic has come a long way, just as mathematics has. It reminds me a lot of Catholics who remain stuck with St. Thomas Aquinas. Western Theravada Buddhists have already made some interesting offerings integrating contemporary western philosophy, applying it to Theravada Dhamma; I'm thinking of Gowans as a good example. I would like to see Mahayana Buddhism follow this example instead of remaining fixated on Nagarjuna.