One "minor" weak point I have with it would be the equivalent of a knowledge base which is more of an osTicket problem than Itarian problem, but I'm positive it can be addressed by changing their add-ons they use. So if I were to use a tool such as MediaWiki or Zoho Wiki for comparison, then ITarian falls behind feature wise for making document management a breeze and also being able to produce doc's via pdf/word/text.
Also having something in mind like IT Glue which can "compile" your client documentation into a file/folder and making it downloadable or shareable is something it can't do but in theory yes you could use the "knowledge base" but that's more or less forking it for something it shouldn't be doing. I see issues of password management running up to.
In the case of my use of it, I'm still seeing more opportunities for me to use 3rd party apps in association with it. Sometimes that's fine but sometimes I lose the "single pane of glass". But honestly, the SPoG is too "marketing" for my taste with not much to show.