One of the most common accusations against Intelligent Design theory is that, while claiming to be science, it is really theology. Usually the people making this accusation see "science" as a good thing and "theology" as a bad thing, so they are effectively trying to discredit ID by associating it with what they see as a pointless and discredited intellectual endeavor. Also, of course, if it's theology it doesn't belong in science class in a public school.
I think that this is a misunderstanding of ID (also of theology). Intelligent Design, at least as defined by its major proponents such as Michael Behe and William Dembski, is the view that there are specific structures (primarily at the cellular/microscopic level) in living things that cannot be accounted for by Neo-Darwinian mechanisms, and which therefore point to the intervention of an intelligent being in the development of life. ID does not require disbelief in evolution in the sense of common ancestry, though of course many creationists (i.e., people who deny evolution) find ID congenial which has led to a common perception that ID is "soft creationism." Behe, I believe, accepts evolution in the sense of common ancestry. Dembski is more skeptical of it. But either way, ID is fundamentally a specific claim about particular mechanisms that allegedly can't be explained by Neo-Darwinian theory.
ID is not the same thing as the philosophical "argument from design" associated with William Paley, though it has affinities with it. And neither ID nor Paley's argument is the same thing as Aquinas' Fifth Way, although the latter is sometimes called the "earliest philosophically rigorous version of the design argument". ID rests on the claim that certain specific structures cannot be accounted for by natural explanations. Aquinas' Fifth Way, like his other arguments for God's existence, rests on the regularity of natural laws, not on anomalous features that can't be explained by them. Aquinas' view is further distinguished from Paley's version of the argument for design (as Edward Feser explains) by the fact that Aquinas is speaking of the natural properties of created things, while Paley equates them to constructed artifacts. Paley's version of a philosophical "argument from design" provides the framework for ID. But nonetheless, it is philosophy or philosophical theology, while ID is not.
ID advocates are often mocked for their apparently dishonest claim that the "designer" might not be what Christians mean by God. Clearly few if any ID advocates think that this is a realistic possibility. But they are making the point as a formal way of distinguishing between the scientific claims of ID and the philosophical religious beliefs that ID advocates hold. According to proponents of ID, science can only tell us that there are certain phenomena best explained by an intelligent designer. Theology and philosophy tell us that this designer is likely to be God. To ignore this distinction is to fail to deal with ID on its own terms.
From the standpoint of "orthodox" science ID is clearly bad science. In the terms formulated by Imre Lakatos, it is a "degenerative" rather than a "progressive" research program. That is to say, it doesn't provide any new, productive insights into the world, but simply interprets the existing evidence in a defensive manner. At least that's how it seems to me, and clearly that's what most scientists think. But perhaps they're wrong. Perhaps Lakatos' criteria are inadequate (I'm more influenced by Kuhn, myself, though from the descriptions I've read it seems to me that Lakatos may provide some needed precision to Kuhn's thesis). Perhaps ID hasn't really had a chance to be productive yet because it's under such constant attack.
Whatever its scientific credentials or lack thereof, the fact remains that ID is not theology. Or if it is theology, it is a very bad form of natural theology which makes God a kind of tinkerer rather than a true Creator.