All that being said, check out this bit from the preface to Degrees of Knowledge:
In truth, Thomism is a common task. One is not a Thomist because, in the emporium of systems, one chooses it as if one were choosing one system among others just as you try one pair of shoes after another in a shoestore until you find a pattern that fits your foot better. If that were the way it was done, it would be more stimulating to cut a system to one's own measure. One is a Thomist because one has repudiated every attempt to find philosophical truth in any system fabricated by an individual (even though that individual be called ego) and because one wants to seek out what is true - for oneself, indeed, and by one's own reason - by allowing oneself to be taught by the whole range of human thought, in order not to neglect anything of that which is. Aristotle and St. Thomas occupy a privileged place for us only because, thank to their supreme docility to the lessons of the real, we find in them the principles and the scale of values through which the total effort of this universal thought can be preserved without running the risk of eclecticism and confusion.
This sort of thing really impressed me as a teenager; now that I'm pushing thirty it raises my hackles. At this point I'm suspicious of any philosophical "system" whatsoever, even one so venerable as Thomism. As soon as one turns one's insights, principles, arguments, and conclusions into a "system" it begins to take on a life of its own, to become a thought-artifact. This seems to be just what Maritain likes about Thomism, which he claims is "organic" and grows through the ages through cooperative work, like a medieval cathedral. But there is inevitably born in its inhabitants and curators the urge to defend the cathedral from outside attack, even if the attack comes only in the form of suggestions for remodeling. It's not clear to me that this defensive posture is the same thing as "supreme docility to the lessons of the real".
This criticism by no means falls on St Thomas himself just because it seems empirically to describe "Thomism". But it's also not clear to me that Thomas either intended to or did build a "system" - and indeed Maritain implies the opposite - or that his particular "thought-world" is a preeminently exemplary vessel of the philosophia perennis in some sort of self-contained and exclusionary way. This is in part why I didn't trade my "Thomist" plate in for a "Scotist" one ("Bonaventurean" wouldn't fit, even if it were accurate!): I'm not at all convinced that there is a "Scotism" or a "Scotistic synthesis", rather than simply a series of uniquely penetrating insights and arguments fitting into and conditioning a common scholasticism - common not in the sense of there being a shared common "system", but a shared terminology, outlook, method, and basic conceptual structure. I don't see any reason why it isn't possible to consider oneself a "Scomist", as one eminent academic I know likes to call himself, or a "Scotaventurean" or "Thomiventurscotist", for that matter. I think it's easier and more sensible just to call oneself a scholastic.
Now this very lack of "synthesis" has led people to criticize Scotus on just this point: his thought is not constructive, but critical, etc, and he's presented as part of a larger story in which the thirteenth century is the age of constructing the great cathedrals of thought and the fourteenth is the age of gnawing at the mortar to see how strong they are. But there's good reason to doubt this story, at least as a story of why the fourteenth century is not so worthy of study as the thirteenth. Everyone would admit that St Bonaventure and St Thomas have a greater power of "synthesis" than Bl Scotus does. But Bonaventure's thought is still closer to Scotus' than to Thomas'. And synthetic power is no guarantee of the truth of any given principle or conclusion. This seems to me the main point. Once we've told ourselves that St Thomas was "supremely docile to the lessons of the real" we're already likely to a) assume that his contemporaries weren't so supremely docile and that b) arguments which if accepted would impair the cathedral of Thomism must come from an inferior docility. As I've said many times before, I think this sort of attitude locates Thomas' merits in the wrong place, needlessly denigrates everyone else, and is bad for the philosophic spirit. If rejecting it means "running the risk of eclecticism and confusion", well, confusion is a constant and unavoidable risk in philosophy. And I have to admit that I don't quite grasp Maritain's horror of eclecticism. I'm not even entirely sure I know what he means.