I thought that the Alternative Cover "Eye for an Eye" was a story in the book, and that excited me because the inference is the Eye People had something to do with the Watchers. But reading the book, that cover had nothing to do with the book itself, so that disappointed.
What this book does show is that the succession protocol of the Man on the Wall is not as thorough as one would imagine. We now see what Bucky was faced with when we see the story unfolding of how McCord succeeded Stafford, his predecessor, and Stafford wasn't alone either, in the very early days, when the Martians invaded in 1913, because there were like 6 other Men on the Wall at the time, but the Entari whittled them down to just Stafford by 1931, when McCord was rescued by Stafford. 1943 saw the succession of McCord from Stafford, when Stafford appeared to be mortally wounded and walked away leaving the job in the hands of the young McCord.
What Bucky is left with is what McCord was left with. Just the diarys of his predecessors and nothing else. So Bucky would have to read through Furys diarys and gleen from that what the threats are around the corner, and, the processes of what to do to hunt for the next ones.
The Annual introduces the race of the Entari, but we don't know if Fury had wiped out their threat completely in the intervening years. The problem is, is that the Entari are a vicious race of Earthling killers who hunt for slaves, and McCord had been a party to an autopsy on an Entari, so he learnt how the Shadow invisibility worked, and was able to utilise that skill to kill a pack of Entari attacking Stafford. There is an opportunity to bring the Entari back with the Winter Soldier series.
A curious episode happened at the end of the book as Stark was welcoming Fury to the Helicarrier for the first time in 1968. The editor missed that it wasn't Howard Stark that accompanied Fury, but Tony Stark, but we can overlook that. If it was Tony Stark who accompanied Fury, then Tony knew Fury was the Man on the wall because Stark asked Fury why he hadn't reported in, in the last few months. Then we cross to the satellite in Earth orbit and an LMD telling the real Nick Fury that LMD 1 wasn't answering Starks question, so Fury already had LMD'S before SHIELD made casts of him for LMD'S, in the first Appearance of SHIELD in the comics. This tells me 1) Tony Stark was always aware Fury was practicing assassinations in outer space, and 2) That Tony Stark knew and probably made LMDs for Fury before SHIELD. And that probably LMD's were alien tech of some sort.
Was this book worth it?
We learnt there was a deeper history to the Man on the Wall than we even realised. We learnt Tony Stark was maybe aware of this. We learnt that LMDs didn't come out of thin air. I liked that McCord was a solitary, lonely, figure who never had family ties, and this made it easy for him to do what he does. He was the Ghost who walked. The John Walker of the Marvel Universe. As to whether this adds anything to the MU? I'd have to think deeper about this than I have so far. President Teddy Roosevelt set them up to do this duty in secret, from their very earliest days, so even back then, there was some need to have this duty carried out.