Merc was probably my personal favorite New Universe title. Particularly in the early issues, the creative team was excellent, and the book represented—at least for Marvel—a broad departure from its usual capes-and-tights fare.
The book was about a mercenary, with no powers, and the various commando missions he undertook, and the 12 issue series actually ended with his death. Other than The ‘Nam, which was based in reality, Marvel wasn’t doing “realistic” books.
This one was a nice change. Nowadays, there’s lots of books like this (but not many at Marvel), but in the 1980s it was a pretty fresh concept.