Biggie was/is overrated in my opinion, while he had some decent ish alot of his stuff (in my opinion) was whack, he had some hits though and Kick In the Door for one was dope.. I wouldn't say that Tupac was overrated ever, he had different values, it depends what you're into.. Tupac was the first rapper to really talk about his life and all of that, import it to his music.. He had a lot of emotional value and it wasn't just the rapper though, people loved the person, there was always a lot of crap going on around Pac.
Nas is decent too, he's got a lot of good-ish and I wouldn't say he's overrated.. I mean when Illmatic came out he was but he's not bad..
Most overrated emcee ever would be Lil Wayne and a few others.. Jay-Z was pretty good back in the day and a great freestyler, LL had some good ish too but both have gone commercial these days..
what?