Most people today know little of him, and in his time, he wasn't the hero of the market squares either. But that only obscures the fact that Thomas has contributed a lot to shaping the intellectual culture of Europe.
Casting aside his obvious achievents on orthodody, he has made rational, deductive argument the ultimate in intellectual activity. That many generations to follow did little but cite and interprete him does not defeat the example he has given, and which surely has been a paradigm for Rennaissance and even Enlightenment thinkers to come, consciously or inconsciously. Thomas was the chain link which connected medieval Europe through the Church Fathers to the ancient Greek thinkers, by applying the same methods as they had done.
Moreover, with his definitory fury in the theological field he has so clearly defined the right doctrine, as hardly anybody had desired since the old church had to disctance itself against schisms before the central creeds were fixed. Now Thomas had revisited this theme without need. As his writings were taken for granted, this implied little freedom of thought for the Christians, but also the duty of the church to take care of religious dissidents.
It is noteworthy that there has not been any signifant "anti-Thomas" school in his time. That made his central ideas so influential, but at the same time common knowledge (among the educated) and self-evident. This is particularly important for the topic "rationality". After Thomas, it was at least in principle clear that religion had to be able to withstand a rational argument! This is a completely non-obvious axiom. Thus he chose the arms with which the reformers and later on the Enlightenment Philosophers would duel with the church.
Of course, not all of this would miss if a genius like he definitly was had not been in his place; his teacher, Albertus Magnus, had already prepared many of Thomas' later doctrines, and the scrupulous way of defining and determining was a fashion well before him, and also outside the monasteries*. But the effect would certainly be smaller without such a central and, at first, unquestioned figure.
*For instance there are regulations on how to plant a castle garden for which modern beaurocrats and their trading rules are hardly a match.