(I originally read these comics in early October 2015)
I did plan to take a lengthy digression from DeFalco's and Frenz's Thor run by reading Marvel's massive 'Acts of Vengeance' line-wide crossover that took place in summer 1989 and to which three Thor issues were dedicated. However another big event, 'Atlantis Attacks,' mostly told in that year's annuals, concludes just before 'Acts of Vengeance' kicks off.
I can't be arsed providing much of a summary. It's an artificially extended tale that doesn't really reward the time spent reading it. Heroes pop in and out of the ongoing plot for just as long as their annuals last (the Surfer, the Punisher, the X-Men and Daredevil aren't seen again after their respective chapters), so there's a disjointed feel to it. The primary antagonists are the Deviant High Priest Lord Ghaur (mistakenly referred to as a 'pervert' by Ben Grimm for one of the story's few laughs) and Llyra, an underused Sub-Mariner villainess.
The good thing about these events/crossovers is that even if one chapter doesn't appeal (for example, I have little affinity for the New Mutants characters), there are different characters to look forward to in upcoming chapters. Some of the chapters were entertaining enough in isolation. Also, a story like 'Atlantis Attacks' provides a good snapshot of where the publisher was 'at' at that given point in time.
As an extra, here's Mike Mayhew's gorgeous original art for the cover of the Atlantis Attacks Omnibus:
Silver Surfer Annual # 2, Iron Man Annual # 10, Avengers West Coast (1989) # 56, Marvel Comics Presents (1988) # 26, X-Men Annual # 13, Amazing Spider-Man Annual # 23, Punisher Annual # 2, Spectacular Spider-Man Annual # 9, Daredevil Annual # 5 (mistakely labelled as # 4), Avengers Annual # 18, New Mutants (1983) # 76, New Mutants Annual # 5, X-Factor Annual # 4, Web of Spider-Man Annual # 5, Avengers West Coast Annual # 4, The Mighty Thor Annual # 14 and Fantastic Four Annual # 22 are collected in:
Hardcover:
Avengers West Coast (1989) # 56, Avengers Annual # 18 and Avengers West Coast Annual # 4 are collected in:
Hardcover:
Avengers West Coast (1989) # 56 is collected in:
Softcover:
Marvel Comics Presents (1988) # 26 is collected in:
Softcover:
X-Men Annual # 13 is collected in:
Hardcover:
Softcover:
Punisher Annual # 2 is collected in:
Softcover:
New Mutants Annual # 5 is collected in:
Hardcover:
X-Factor Annual # 4 is collected in:
Softcover: