I agree with Shiro, he said it pretty good.
To me, the lyrics must have some sort of meaning, not just a collection of punchlines (with rare exceptions). The artist much be able to write in and rhyme while being able to express a clear idea / emotion at the same time.
However, if the lyrics are great but the beat is lame, then I will most likely skip over that song.
The same thing goes for the rapper's voice. A song could have a hot beat, awesome lyrics, but if the rapper has an effortless, emotionless, or annoying voice then I skip the song. For Example, 3 A.M. I love the beat, like the lyrics...just hate the voice....skip...
So yes lyrical content is very important to me, but lyrics are merely a small component of a bigger functioning machine.