As a Poet, his compositions have great inequalities, some of them being possessed of every requisite to be sought after in the most perfect composition, while others can hardly be considered as superior to the productions of mediocrity. Much of the merit of his Epistles to Eumenes, to a Young Critic, and to John Wilkes, Esq. consists in a spirited consciseness, a lively representation of characters, and a certain sprightliness and turn of wit, which are always pleasing. But they seldom rise into a high strain of poetry, and are sometimes deficient in grace and ease. The Epistle to Eumenes, is rather too satirical for the subject. In the Epistle to Taste, he is severely satirical on all pretenders to wit; but he does not treat the subject in so masterly, nor in so poetical a manner as Pope had done before him. In his Day, he seems not to have intended rising much higher than prose put into numbers. His Winter Piece, in imitation of Shakspeare, has more elevation, but in a turgid and inflated performance.
His Art of Preserving Health, on account of the reputation it has so justly acquired, precludes all criticism. It is of the highest species of didactic poetry, and of a merit and character so great, as to rank with the compositions of Lucretius, Horace, Virgil, Vida, Boileau, Akenside, Dyer, and Grainger. Akenside has attempted the most rich and poetical form of didactic writing in his Pleasures of Imagination, and in several parts, succeeded happily, and displayed much genius. Armstrong has not aimed at so high a strain as Akenside; but he is more equal, and maintains throughout a chaste and correct elegance.