Eh, I don't know if I completely agree with that notion. It might be true to a certain extent, mainly because many of today's movies are variations or continuations of the same concepts we've seen time and time again. This makes some movies seem unoriginal and unimpressive, because we've "been there and done that" before, even if they are technically solid films.
The reaction to certain films can (and should) hinge on the time they were released, what they presented to audiences, the impact the film had on audiences along with cinema as a whole, and some classics like JP represent a "perfect storm" of factors coming together. Would Jurassic Park get picked apart more if it were released today instead of 20 years ago? Probably, but based on the nature of today's cinema, they probably wouldn't have produced a movie that closely resembles what we know as Jurassic Park.
With JP, you had a director in the prime of his filmmaking era, a strong cast that elevated the characters as they were written, the perfect blend of practical and digital effects that pushed the boundaries of what people knew to be possible then, an incredible musical score, and of course, the benefit of presenting audiences with a concept they had never seen before. Furthermore and for all these reasons, it was a great film that influenced many of the blockbusters that followed it and was undeserving of harsh criticism or discontent.
Another important thing to consider is that while it might seem like movie fans are now more jaded, overly critical, and harder to please than before is that there now exists an outlet (the Internet) where people like us (or anyone) can publicly voice their opinions on any and all movies that are released or have been released in the past, whether it be through any of the social media platforms or community forums like this one. Today, anyone has the opportunity to be a "critic", whereas that opportunity didn't exist in the past.
People walking out of The Lost World or Speed 2: Cruise Control might have been able to talk to their friends or family about how/why they thought the movie sucked and wasn't as good as the original. They were able to pick it apart with their work colleagues the next day or could discuss it over the phone while having a conversation with someone, but they couldn't get online and write a post that expressed their thoughts to their hundreds or thousands of Facebook friends and Twitter followers. They couldn't make a Youtube video to mock the movie and rip it to shreds. They couldn't find hundreds of critic's reviews from every media outlet in the country collected in one place that was available for them to view with one click of the mouse.
I do think it's harder to produce a blockbuster today that is widely considered to be good or great, mainly because (as I said) so many more movies are released yearly now, we've already seen just about every kind of movie you can think of, expectations are higher than they used to be thanks to the way movies are anticipated and reported on, and it's harder for movies to be "fresh" or innovative.
But with that said, I think the same general rules apply. Audiences appreciate and respond to tightly wound stories, great characters and actors, exciting visuals, and films that either present us with new concepts or take existing concepts and turn them on their heads. Films like The Dark Knight, Inception, The Avengers, Guardians of the Galaxy, Gravity, The Departed, (500) Days of Summer, District 9, Knocked Up, Little Miss Sunshine, Casino Royale, Pixar's Up, and Avatar are recent films that I feel are good examples of this.
