Nas' Def Jam run, for sure. The stage seemed to be set for something truly special. While those first albums were undeniably successful and he proved he still was still relevant (see: the crazy mixtape impact he had at the time) I feel like that first album HHID really missed the mark of what fans wanted. I bumped it a lot. I was in college at the time and have some good memories tied to specific songs but I feel like the stage was set for Nas to drop a classic album and instead he just dropped something that became typical for him on the label: a "meh" album that nobody really remembers.
As others pointed out in the thread...he was working with Premo again yet it never materialized. He was working with Just Blaze but it never materialized. We got 1 great Kanye produced track (Still Dreaming). Meh Dre/Storch stuff. I feel like that album would have been perfect to kinda do a tour of rap shyt, from 80s boom bap to west coast shyt to 90s east coast shyt to the dirty south and then to the present. I'd imagine that may have been the vision Nas had too but it didn't come out well .Premo could have helped with that, man. Large Pro could have helped with that. Dre could have helped with that (with better beats). Just a miss...
Same with Untitled. I thought we'd get some gutter shyt but instead it's an unfocused collection of songs and half baked concept records. Once again that was an album that Premo would have been perfect for. Maybe add in some Dilla type shyt. Oh well.