I really enjoyed Iron Man. Yes, there is something to reward those who hang around for the end of the credits.
Plotwise, it was fairly predictable, but that’s due in part to the fact that I know the form the writers are working within. EVERYTHING is fairly predictable for me these days, and I wouldn’t have it any other way. It didn’t hurt the Iron Man film at all, because the character interactions, the fight scenes, the SFX, and all the rest of the details were so much fun.
Plot holes? Sure. It’s a superhero film, after all.