I would say that the presence of annoyingly stereotypical characters is precisely that. A Priestess of Shar absent depth, a Gith warrior who is unsurprisingly chaotic evil to the point of behaving as a monolith, a vampire spawn who creeps about in textbook fashion. I can go on, but my point of contention with the supporting characters is that they behave so woefully generic, that it's as if somebody just pulled them out of the sample sections for the PHB (or MM, depending on what character you're referring to). Maybe individual quirks will be better exhibited later on in the game? Who knows? But at its current state, that is a point of concern I have regarding the characters, as they sit. This is a feedback section, after all, and this is the feedback I am providing.
Mary sue is a particular trope mate, not a stereotype. As for the characters YMMV. An aristocratic vampire is a trope sure, the Gith companion doesn't come across as chaotic evil to me. She comes across how I'd expect a gith warrior to come across; obsessed with their mandate and hostile to those that get in her way. The Priestess of Shar clearly has depth to her character as you get to know her a bit more. Luckily if you don't like these characters they're not the only one on the roster.
