The thing I didn't think was done well in ENT was the exploration.
It seemed to me that the universe had already been discovered in ENT. In TOS in some episodes you got the impression that Kirk and his crew were the first beings from the Federation out there.
In ENT while the overall mission was one of discovery I don't recall a time when they were discovering anything new. I think Mayweather's Mum had beat the NX to many places. And of course the Vulcans and Andorians were always there before them.
I agree that the NX-01 was largely exploring "known space", but it was known to the Vulcans, not the Terrans! There were plenty of firsts for the crew to experience before venturing outside what would eventually be Federation territory.
I agree the "boomers" complicated the issue - the extent and limitations of their travels were never really explained.