Hendrix is a fine guitarist. If you ask random people on the street who the best guitarist ever is, Hendrix is the name you'll hear more often than not. I can name several who were better than him, however. Thus, even though I have no problem with his excellent guitar work, I have to talk down on him a bit because of the tendency to be oversold. Unlike Zeppelin, Hendrix actually is quite good, and so is (or was, as the case may be) Eminem.
What the analogy doesn't address is the way Eminem tends to either get way too much credit or none at all.