The definition given in Chalmers (1995, facing up to...) following Nagel, i.e. using the linguistic construction "what it is like", is incomprehensible and ill-defined. I believe this is the origin of the term "hard problem". Some other arguments for the existence of a hard problem build on the dogma that "philosophical zombies" are conceivable (which we can deny by saying they aren't). Others depend on inverted qualia thought experiments, which we can deflate by denying that inverted qualia are possible at all (or by denying that "qualia" is a coherent and well-defined concept). If there's an unambiguous and clear explanation of the concept of "hard problem of consciousness", or a clear argument for the existence of such a problem not built on shaky assumptions, I'd love to hear it.
By the way, there is a whole line of debate on the sense or nonsense of the ever-present "what it is like" phrasing:
>‘What it is like’ talk (‘WIL-talk’) — the use of phrases such as ‘what it is like’ — is ubiquitous in discussions of phenomenal consciousness. It is used to define, make claims about, and to offer arguments concerning consciousness. But what this talk means is unclear, as is how it means what it does: how, by putting these words in this order, we communicate something about consciousness. Without a good account of WIL-talk, we cannot be sure this talk sheds light, rather than casts shadows, on our investigations of consciousness.
(Jonathan Farrell - ‘What it is Like’ Talk is not Technical Talk)
By the way, there is a whole line of debate on the sense or nonsense of the ever-present "what it is like" phrasing:
>‘What it is like’ talk (‘WIL-talk’) — the use of phrases such as ‘what it is like’ — is ubiquitous in discussions of phenomenal consciousness. It is used to define, make claims about, and to offer arguments concerning consciousness. But what this talk means is unclear, as is how it means what it does: how, by putting these words in this order, we communicate something about consciousness. Without a good account of WIL-talk, we cannot be sure this talk sheds light, rather than casts shadows, on our investigations of consciousness.
(Jonathan Farrell - ‘What it is Like’ Talk is not Technical Talk)