Kemble was the next great actor to inherit Garrick's mantle. Garrick had revolutionised acting with his realism, portraying emotions as one would imagine seeing them, (he was famed for his still portrayals of emotions) anger was instantly recognisable for instance. Kemble was very different and indeed to my mind, much more modern.

Many times he would build the character slowly, revealing little emotion, almost distant to the things happening to him building until the tension at the climax was intense.

Michael Peter Bolus is very eloquent on the subject:

In Paradoxe sur le Comedien, Denis Diderot writes: "To move an audience, the actor himself must remain unmoved" Of all the great English stage—actors, perhaps the one most exemplary of Diderot’s prescriptive musings was John Philip Kemble.

In his Critical Essays on the Performers of the London Theatre (1807), the English critic Leigh Hunt includes the following description of Kemble on stage:

"For the expression of the loftier emotions no actor is gifted by nature with greater external means. His figure though not elegant is manly and dignified, his features are strongly marked with what is called the Roman character, and his head altogether is the heroic head of the antiquary and the artist. This tragic form assumes excellently well the gait of royalty, the vigorous majesty of the warrior, and the profound gravity of the sage; but its seriousness is unbending; his countenance seems to despise the gaiety it labours to assume, and its comic expression is comic because it is singularly wretched."

Kemble was one of the nineteenth century's last stalwart practitioners of an acting style still stubbornly described as "classical"; a style concerned with such troublesome concepts as stateliness, dignity, and grace as opposed to passion, bombast, or "realism of emotion" (Brockett, History of the Theatre 407). Often referred to as the "teapot school" of acting (because of the actors' preferred posture), Kemble's style was frequently criticized for its stiffness, artificiality, and distanced coldness. Yet his sober, measured delivery was in strict accordance with the more fundamental principles governing Classicism; principles which favored the universal over the particular, abstraction over specificity, and the communication of general, timeless truths over lifelike reproductions of psychological intricacies.

Kemble's acting style was soon to be eclipsed by the pyrotechnics of the Romantic school, whose adherents included such popular contemporaries as George Frederick Cooke and Edmund Kean. Cooke and Kean placed no value on what they believed were antiquated notions of grace and dignity, and their willingness "to cringe or crawl on the floor" (Brockett, History 407) excited audiences for whom this new approach was both novel and revolutionary. Because Romanticism’s expressed aims were to upset the staid traditions of Classicism, the freshness of the Romantics' interpretive methods were embraced as emancipating. It is perhaps more useful, however, to regard Kemble's craft not as an evolutionary stepping-stone toward a more sophisticated or effective style of acting, but rather, as belonging to an aesthetic philosophy at fundamental odds with more prevalent creative currents.

Though his reputation was as one of the premier actors of his generation, he did not escape some rather harsh criticism of his manner of preparation and delivery. The above-quoted Leigh Hunt, for example, though sporadically complimentary of Kemble’s talent, could be a ferociously vicious detractor:

"He appears to submit everything to his judgment, and exhibits little of the enthusiasm of genius…he sometimes turns from one object to another with so cautious a circumflexion of head, that he is no doubt very often pitied by the audience of having a stiff neck. His words now and then follow one another so slowly, and his face all the while assumes so methodical an expression, that he seems reckoning how many lines he has learnt by heart…he does so dole out his words, and so drop his syllables one by one upon the ear, as if he were measuring out laudanum for us…he is always stiff, always precise, and he will never, as long as he lives, be able to act anything mad unless it be a melancholy mad statute."

William Hazlitt hastened to add that he moved slowly, from pose to pose, "with as much care as if he were a marble statue and as if the least trip in his gait, or discomposure of his balance, would be sure to facture some of his limbs"(Shattuck, Kemble ix). Some believed that Kemble's "deliberation and solidity, statuesqueness, abstraction, and unrelieved, humorless dignity"(Shattuck, Kemble xii) might appeal to those who subscribed to decidedly neo-classical conceits; but even Kemble's admirers conceded that "he sometimes sacrificed energy to grace, that by overly precise and even distribution of emphases he enfeebled what should have been vehement, and that by too elaborate a building up of an action he often lost the surprise of it (like a clock that clicks a warning that it is about to strike the hour)."(Shattuck, Kemble xii) As the Romantic zeitgeist began to build momentum, Kemble's acting style slowly began to fall out of favor.

In addition to staging the plays, Kemble would prepare detailed "promptbooks," not merely for use by the company's actors and technicians, but for sale to the theatre-going public.

The promptbooks also offer interesting insights into Kemble's working habits and methods of preparation. He would pore over scripts and "was studious to a fault, weighing every syllable and its accompanying action with a scrupulousness verging on pedantry; and he was determined to communicate the total result of his study that his rate of playing was oppressively slow."(Shattuck, Kemble ix) The books also reveal his penchant for antiquarianism—the practice of attempting historical accuracy in all aspects of scenic and costume design. This inclination is rather paradoxical as it runs contrary to Classicism’s insistence on general nuance and suggestion as opposed to localization and particularities.

On the occasion of his retirement, William Hazlitt wrote the following:
If he had not the unexpected bursts of nature and genius, he had all the regularity of art; if he did not display the tumult and conflict of opposite passions in the soul, he gave the deepest and most permanent interest to the uninterrupted progress of individual feeling; and in embodying a high idea of certain characters, which belong rather to sentiment than passion, to energy of will, than to loftiness or to originality of imagination, he was the most excellent actor of his time.(Donohue, Kean 146)
Hazlitt’s notion of the "regularity of art" may strike an odd note with modern readers who have been inculcated with still prevalent Romantic notions of artistic inspiration, the individual genius, and the primacy of the imagination. There was a time, however, when art was judged by its calculated sense of balance, order, and harmony; its measure, cognition, and wholeness; its nuance, subtlety, and suggestiveness; its timelessness and universality; its exhibition of a mastered set of acquired skills. Kemble's craft, often labeled artificial, stiff, monotonous, and studied, sprung not from an inferior understanding of the actor's function, but from an altogether different aesthetic sensibility; a sensibility similar to those espoused not only in Diderot's later writings, but in tracts by such modern theorists and practitioners as Arthur Symons, Edward Gordon Craig, Bertolt Brecht, and even, one might argue, David Mamet—a sensibility which favors calculation over instinct, detachment over emotional intimacy, and symbolic gesture over idiosyncratic mannerisms.
John Philip Kemble exhibited a willingness to subordinate his own emotional torrents in favor of prefabricated design, precision, and unwavering consistency.