The film is, basically, a step-brother to The Goonies. Produced two years later, and with the same spirit of "group of friends band together to face a challenge greater than them", Monster Squad may not have lived up to the success of Goonies, but it remains as endearing. The film focuses on a group of friends who, when the classic Universal Monsters* show up (Dracula, Wolfman, The Mummy, Frankenstein, and Creature From The Black Lagoon), they must defend their town, and themselves, from the ghastly group and its plans to take over the world.
I love it, but I'm not sure how much of that is nostalgia, and how much is that it is legitimately good. The acting is what it is (kids are always hit or miss), and, it was the 80's, so a lot of those movies were being churned out with less focus on quality and more focus on whether or not they could get an audience to show up for the premise. I love it, though, and it will always hold a special place in my heart.
* I recognize that Dracula, etc, were not invented by Universal Pictures, but their visual portrayal in this film seems highly influenced by those classic films.