Is this one of those threads where people answer the question and you argue them down?
Ghostface Ironman and Supreme Clientele
The hard thing about this question is that Illmatic is possibly the greatest debut EVER, and to even contend you gotta be either Biggie, Rakim, or have some shit that changes the face of music, i.e. a Chronic or a 36 Chambers. IWW to me was great, but it came up short to Nas's standards. Almost every artist mentioned here had a strong debut, but stepped up big time in their 2nd album.
Speaking of Rakim (with Eric B), Paid In Full and Follow The Leader is up there too.