I could be snarky and say that I love The Blob because "It creeps and leaps and glides and slides across the floor". Honesty could prevail and I could simply admit how much I love B-movies (oh boy, do I!). Still, the answer to the titular question is quite a bit more nuanced than a simple singular answer could account for. Let's examine the parts that make up the whole that is The Blob.
Filmed in 1957, The Blob was intended to be the B film in a double bill with I Married a Monster from Outer Space, but it turned out that more people were paying admission to watch a gelatinous monster absorb unfortunate townsfolk and so their roles were reversed. It had a very modest budget of $240,000 and featured a then unknown Steve McQueen, who famously took a flat payment of $2,500 dollars instead of ten percent of the film's gross. He didn't think the film was going to perform well; it made ten million dollars at the box office. It was the first movie role, in a career that would span decades for Aneta Cirsaut and the last role of a character actor who began in the silent era of cinema, Olin Howland. It's this mix of well travelled character actors and upcoming young actors that gives The Blob a great small town feel, to which many could relate and some long to return to, but which didn't feel forced. The side characters however ARE goofy and in some cases, poorly acted (I'm looking at you Mr. Fire Brigade Chief), to the absolute delight of Blob fanatics.
To complete the small town feel, Valley Forge Studios scouted filming locations in the surrounding towns. It was this masterstroke that really gives, what is otherwise a goofy monster picture, it's grounding, it's heart. In particular, The Colonial Theatre in Phoenixville, Pennsylvania has become a fixture of Blob fandom. It's been restored to it's majestic 50's kitsh and holds an annual Blob-Fest celebration, which the whole town gets in on. The Downingtown Diner, location of the climactic scene, doesn't quite look the same, but I'm told the famous basement is still much as it once was.
Still, if this were all The Blob had going for it, we'd likely not be discussing it with the same reverence. What is it about this film that so captures our attention and fond recollection? Teenagers, terrorized by a monster, who try to warn adults, who refuse to believe them. That could be applied to an incalculable number of films. Where this one is different, I feel, is in it's portrayal of both the teens and the adults. Unlike many of the "teenagers in rebellion" pictures coming out at the time, the teens in The Blob aren't "stupid rebellious". Certainly they race their hot rods, they play jokes on each other, but it's never malicious or mean spirited. The adults aren't quick to trust the teens, but some actually do listen and consider what is being said, quite unlike most other films, especially of the horror and science fiction genres. There's a feeling of playfulness between the cops and teens, rather than hate and spite, which otherwise infects the entirety of both genres now and is in fact completely expected. And the film pervades hope as well. Hope that by banding together we can save ourselves.
There's plenty of conjecture that the message of The Blob is of the dangers of Communism and defeating it with cold(what an ironic conjecture). I don't buy it. To quote Tim Curry from Clue, "Communism is just a red herring". Besides, if you started out clear, it stands to reason that you too would become more and more blood red as you absorbed squishy human-fodder.
I'll stop gushing now. The Blob is a fun flick. A really great example of 50's drive-in monster cinema. Check it out and let me know what you think. See you at Blob-Fest!