Oh well. At least it wasn't awful.
Two words spring immediately to mind: formulaic and shallow. Not that there's anything wrong with being formulaic and shallow - indeed many formulaic and shallow pictures nonetheless rake in the big bucks - but formulas become predictable, and predictability kills immersion unless the characters are interesting enough. Here, they weren't. They just weren't developed enough to make me care.
Batman Begins follows much the same formula, but in that film, we had real character depth and conflict. We dig into Bruce Wayne's motivations. We don't do that with Tony Stark, so we don't care about him. The film becomes a vehicle for impressive but vapid special effects and an intolerable string of ham-handed set pieces (accompanied by obnoxious, repetitive, heavy metal riffs) showing them off.
You slavishly follow a formula so you don't have to think about plot. Use a plot with an established success rate, dress it up in the latest SFX bling, and rake in the dough. It really isn't art.
It had some good moments. Even some of the set pieces (most of which made it into the trailer, which, having seen the film, I can now say was an absolute masterpiece of editing and marketing) were nice, even if overdone. It managed to keep my attention, if superficially, and didn't stagnate. My favorite moment has a fake-bald Jeff Bridges yelling at Unnamed Also-Fake-Bald Scientist that Tony Stark was able to built some cool techy thing in a cave with spare bits, and the scientist responding "But I'm not Tony Stark!"
I hated the score because it was overwrought, intrusive, and added nothing to the experience. And Gwyneth Paltrow got royally screwed by the main unit focus puller during the balcony, almost-kiss scene. And there were more continuity issues (e.g., Gwyneth's shoes mysteriously change while she's sneaking into Stark's office at the end of Act IV) than there ought to have been in a film of this budget. They skimped on principal photography almost as much as they skimped on the plot. Just goes to show that having a big post budget for effects can't make up for shoddy source material.