I can't imagine it being an "unqualified hit right out of the gate" as you say. It became that, but early on, it was an unknown. Our look back is colored by all that has come since TNG first debuted; it may be hard to remember what it was like when all there was of Trek was TOS and the TOS movies.
TV Obscurities wrote:
None of the syndicated programming premiering in the fall of 1987 was as highly anticipated as the two-hour premiered of Paramount Televisionís Star Trek: The Next Generation. Proving that within the television industry you can go home again, Gene Roddenberry brought his unique vision of the future back to the small screen, starting the week of September 28th (because syndicated programs air at different times on different days in different areas of the country there is no set airdate).
Overall, in Nielsenís fifteen major markets, the premiere averaged a 21 share and, more importantly, an impressive 300% improvement in share over the comparable year-ago numbers in those same markets. Ratings for the series were so good, in fact, that Paramount renewed Star Trek: The Next Generation for a full second season in November of 1987.
An unqualified hit right out of the gate.
I don't see it that way. I see it as highly anticipated, heavily promoted, but not an "unqualified hit." Out of the gate, it was a huge unknown, with an uncertain future - even the actors knew that.
It was a big, high profile gamble. That's why the debut numbers were so high. There were many questions swirling around it, many doubts, many questions.
TNG stumbled, soared and fell through its first two seasons; it became a hit in its third season, as it found its own footing, came out of the writer's strike-affected second season, and outlived its predecessor.