"A Beautiful Mind" with an unhappy ending. That comparison may or may not be agreeable to you, but overall I enjoyed the movie although it was not one of Scorsese's nor DiCaprio's best films. I have to admit I spoke to some friends wandering outside the cinema afterwards who asked if I recommended they see the movie, and I honestly couldn't tell them yes or no. a good movie, not a great movie.
It was good to see Indy again, but this was this the weakest of the 4 movies. The script just wasn't that great as compared to Raiders or Last Crusade, and was even weaker than Temple of Doom. Despite knowing this, I still would go see Crystal Skull, as it is entertaining, but without a better script this series has lost it's edge - I just was never that worried about the fate of the characters during the whole movie.
This is a good movie! Don't let the fact that it's super-hero genre put you off, if you are so inclined. This is a really fun movie to see, and I don't believe you need to be an Iron Man fan or nostalgic over the fact you read a few Iron Man comic books in the past to really enjoy this flick. Give it a chance. I predict you will at least like it.
As for the Iron Man fans, you will love it! I think this was the best adaptation for a Marvel Comics character yet (O.K., Spider-Man is a very close second). And the fans can even guess at some of the plot of the sequel (Rhodey saying he'll wear the suit next time is a clue).