'It posits a single, almighty, intelligent agent, not vague "forces of nature;" not a concoction of natural selection, random mutations, unguided forces, etc.'
And that is its biggest problem - no scientist has observed this "single, almighty, intelligent agent", OR any evidence that he/she/it exists or took any action.
However, scientists have repeatedly observed natural selection, random mutations and unguided forces.
Thank you for very clearly stating one of the main reasons ID is emphatically NOT science.
I assure you that if you produce the "Intelligent Designer", and/or ANY *believable proof* that he/she/it actually transformed or created species on Earth, you'll win the Nobel Prize ten times over.
The evidence for an intelligent designer is indirect, much as the evidence for the director in a play is indirect while watching the play. There is ample evidence of intelligent design, as demonstrated by the ubiquitous presence of organized matter that behaves according to predictable laws.