First of all, these songs are tight. Tupac was doing what Dr. Dre does now. He recorded hundreds and hundreds of songs for himself, and for his albums, picked the very best and released them. Like Dr. Dre, Tupac still has some ill unreleased material. It's not that these songs are wack, it's just that Pac didn't pick them at the time.
Many of 2pac's greatest songs are still unreleased: Soon As I Get Home, They Don't Give A Fuck About Us, etc.
Tupac recorded several hundred songs for Death Row in 1996. Of that, he was going to pick 8 for his Makaveli EP(later upped to an LP). There's plenty of material left, and you know almost all of it's tight. There's way more than 100 unreleased Tupac songs, and some of them are straight classics.
This album that will be released this year was supposed to be Tupac's last... but then when the estate was asked if this was the last album of unreleased Death Row material, they answered "probably not."
We'll have plenty of Pac in the future... don't worry.