House of Vengeance
The Weakest Point by John Byrne is the first part of the Acts of Vengeance storyline and features Doctor Doom launching an attack on Avengers Island. Despite it being an issue of Avengers, the Avengers themselves don't really feature except for their newest member Quasar as well as oft-forgotten Stingray (who owns Avengers Island) and many of their supporting cast such as Guardsman, Mechanaut and Peggy Carter feature heavily.
This is just a good story. From a time when Avengers books weren't just Captain America charging forward with Iron Man and Thor yelling "Avengers Assemble" on double splash page after double splash page. While this obviously isn't the best example of a good Avengers issue since it really only features Quasar in a substantial role, it's a good issue because it fleshes out many of the people who help the Avengers and shows that they are just as brave as the superheroes. It's kinda a standard message for a comic but it's backed by being part of what is just a good issue.
The story ends with the enemies succeeding and the Avengers headquarters being destroyed despite the best efforts of Quasar and company. It's cool to see the Avengers basically fail due to their inability to respond to the emergency call and this kinda logic with Captain America, Thor, etc. being unavailable because they have their own books and stuff really just is ignored in modern day comics (Captain America was chasing Zemo around the world and Thor was presumably just feeling lazy). People who buy into new Avengers garbage don't seem to understand that for the first 500 or so issues, the Avengers weren't about the big names, it was about heroes. Some of them happened to be big names, others (like Quasar) weren't. Watching Guardsman, Mechanaut, Peggy Carter and Quasar try to fight off Doctor Doom's army is far more interesting than reading how Iron Man has some amazing ANTI-DOOM ARMOR or some crap.
This is an Avengers issue from one of my favorite Avengers periods - the John Byrne era - and even though this is a strange inverse to Byrne's tendency to have almost every Avenger in his issues, it's still enjoyable. Yes, Avengers headquarters being attacked by villains was done only 20 issues ago with the critically acclaimed Under Siege, but having their headquarters destroyed is a good enough way to kick off a crossover and basically have the Avengers hindered somewhat. Although, you can't help feel sorry for poor Stingray who's island was destroyed because he offered it to the Avengers only for them to pretty much ignore him now that he no longer has something they can use (they later let him rejoin the team because they want to use his submarine...and kick him off when they're done on that mission!). Yes, this is another good issue from Byrne's run definitely and a great first part to Acts of Vengeance.