To give you a point of reference, I'm 34 years old, I saw "Raiders" with my dad and my brother during its original theatrical run and I've been a fan ever since. I was thrilled that a 4th movie was in the works, and was hopeful that it would be a welcome addition to the series; after hearing how Harrison Ford, Steven Spielberg and George Lucas had refused to put anything out until they were satisfied with the script, I had only gotten more excited.
I saw the 12:01am showing on Wednesday night/Thursday morning. Oh, boy.
The problems, in my eyes, are this: the script is mediocre at best, and George Lucas is up to his old tricks in putting way too many unnecessary, computer-generated effects and kid-focused action into the film. The first movies -- though far-fetched at points -- had a "real" feeling to them, while parts of this look more like a cartoon or a video game. Some of the humor is way too ham-fisted (though some jokes do work), and the suspension of disbelief that the audience is asked to give is a little bit of a stretch.
It's not a complete failure: there are certainly crowd-pleasing moments (the opening chase sequence, a motorcycle chase through the streets of New Haven, CT), and a few tips-of-the-cap (or fedora) to the die-hard fans of the series. But when the best thing you can say about a movie featuring beloved characters is "It was OK" or "It was pretty good," then there's a problem.
Would I recommend it? Yes, if only so you can judge for yourself. If you're a casual fan and want to see some light, fun adventure for 2 hours, then this should do the trick. If you grew up with the films, know all the lines and want to be blown away with the latest exploits of Indy, then you may be a bit disappointed.