The conventions of Imagism are simple. Imagistic poetry rejects the abstract whole cloth, limiting writers to the use of entirely concrete terms in search of some kind of objective poetic experience. The original Imagists were more or less writing in rejection of the swooning language of the Romantics and other Victorian poets, hoping to achieve a simpler and ultimately more universal method of conveying human experiences in verse. In contrast to the likes of Wordsworth and Coleridge, the Imagists abandoned any talk of love, beauty or other wholly subjective terms in favor of close-up descriptions of material artifacts of life. It was all wheelbarrows, bricks and belt buckles, and Roethke sitting in his garden.
There's nothing inherently wrong with the original Imagist movement. After all, its accessible language likely had more influence on the wild Beat poets of the 40's, 50's and 60's than anyone would like to admit. The problem is with the reactionary pointlessness of New Imagism. Sick of Ginsberg and other raving upstarts, the academics of the 1980's decided that the best way to salvage American poetry from the drug-addled gutter was to jump back eighty years with no real concept of the inherent limitations of the Imagistic form.
Abstract terms ought not to be stricken from poetry forever. Yes, when a poet becomes too reliant on ideas like anger or joy his or her work tends to lose punch, but there's also no reason to insist on basing all poetry on what basically comes down to materialism. Words will never be able to do what visual art does with the same level of impact. It's as absurd to insist on Imagism next to, say, painting as it is to prefer descriptions of flavors instead of actually eating real food. Abstracts are unique to language. Where a painting may depict what someone may interpret as "love" or a song may convey what someone thinks sounds like "anger", only language can ask people to contemplate those subjective ideas consistently.
Imagism has its place in poetic form. It still ought to be taught in universities and applied as a valid method to new poetry, but it should cease to be the dogma of the academics. That it has been allowed to so dominate the teaching of poetry is as absurd as only teaching organic chemistry to students pursuing biology degrees.