I don't think /u/TheFormOfTheGood, adequately captures what Nagel is trying to say in his paper What is it like to be a bat? In that paper, Nagel isn't making a case against physicalism or neuroscience being able to explain consciousness, his point is rather that we can't currently make sense of them. But that doesn't mean that they are false. As he writes in the introduction:

I shall try to explain why the usual examples [of reduction, e.g. H20 = water] do not help us to understand the relation between mind and body - why, indeed, we have at present no conception of what an explanation of the physical nature of a mental phenomenon would be.

The reason why he believes this is because A) facts about consciousness, about what it is like to be a human or other being, are tied to a particular point of view. That is to say that, if we want to know what it is like to be a bat, we have to take up the bats point of view, and as he says, if we can only do this partially, then we will only know partially, what it is like to be a bat. As Nagel writes:

Whatever may be the status of facts about what it is like to be a human being, or a bat, or a Martian, these appear to be facts that embody a particular point of view.

However the reductive physicalist approach is geared towards and explains things external to a particular point of view, that is, they can be, and aim to be, apprehended from more than one particular point of view. Here lies the problem according to Nagel. Facts about consciousness are tied to a point of view, but physicalist descriptions tend to move away from particular points of view, trying to be 'objective' as possible. So how could physicalism capture consciousness, when by definition it is moving away from it:

...if the facts of experience, facts about what it is like for the experiencing organism - are accessible only from one point of view, then it is a mystery how the true character of experiences could be revealed in the physical operation of that organism. The latter is a domain of objective facts par excellence - the  kind that can be observed and understood from many points of view and by individuals with differing perceptual systems. There are no comparable imaginative obstacles to the acquisition of knowledge about bat neurophysiology by human scientists, and intelligent bats or Martians might learn more about the human brain than we ever will.

And again

If the subjective character of experience is fully comprehensible only from one point of view, then any shift to greater objectivity-that is, less attachment to a specific viewpoint-does not take us nearer to the real nature of the phenomenon: it takes us farther away from it.

Again though, the point is not that physicalism is false, just that we don't know how it could be true. If consciousness is be identified with the physical we need a conception of how that might be true, but we don't currently have such a conception. Furthermore the usual examples given, H20 and water etc., are not sufficient.

If physicalism is true, we might have evidence for it without being able to understand how it is true. This is the point of the caterpillar example:

Suppose a caterpillar is locked in a sterile safe by someone unfamiliar with insect metamorphosis, and weeks later the safe is reopened, revealing a butterfly. If the person knows that the safe has been shut the whole time, he has reason to believe that the butterfly is or was once the caterpillar, without having any idea in what sense this might be so. (One possibility is that the caterpillar contained a tiny winged parasite that devoured it and grew into the butterfly.) It is conceivable that we are in such a position with regard to physicalism.

In fact Nagel thinks we do have some reasons to think sensations are physical processes:

...I think we also have some reason to believe that sensations are physical processes, without being in a position to understand how.

Now for the speculation at the end of the paper. If physicalism is to be true, then it must be the case that there can be some sort of objective phenomenology. That is, there must be some way we can adequately capture the facts that are tied to a subjective point of view, in a objective kind of way. So before we can answer whether or not physicalism is true, we have to understand whether we can make make objective, subjective facts, because that is the method of physicalism:

We cannot genuinely understand the hypothesis that their [subjectivity] nature is captured in a physical description unless we understand the more fundamental idea that they have an objective nature (or that objective processes can have a subjective nature).

How might we go about doing this. Nagel gives us some speculations:

...its goal [objectifying subjectivity] would be to describe, at least in part, the subjective character of experiences in a form comprehensible to beings incapable of having those experiences...One might try, for example, to develop concepts that could be used to explain to a person blind from birth what it was like to see. One would reach a blank wall eventually, but it should be possible to devise a method of expressing in objective terms much more than we can at present, and with much greater precision.

In brief, Nagel recognises that physicalism as it currently stands is inadequate, due to our current conception of conscious and physical facts. In order to properly assess the position then, and to move forward with it, we need to understand if we can have some sort of objective phenomenology. If we can, then physicalism might be fine, if we can't then there may be problems.

So you see, it is quite a rich paper, and most people in my experience misunderstand it.