Harry is the only one of the new characters (I include the ''ultimate versions'' of the original characters in this too) who guess what, he's the only one who feels like a ... character!
Vrissy is a fag version of vriska, that the comic tries to show us as a maternal version of Vriska (due to Kanaya's influence) without losing her bossy trait, but that in the end just well ... she's there
Tavros Crocker is like a kind of a fusion of Jake and John showing us how pathetic this person would be if this being had terrible parents, the idea is that just observing him makes you uncomfortable, and it turns out that he succeeds at it...
Yiffany is a cruel sadistic joke who absolutely no one laughs at it, she isn't a character.
The extras are all forgettable and without charisma.
The Ultimate-Selfs/Whatever (Ult Dirk, Rosebot, Daveboy, Alt Calliope) they're just some boring fucking assholes to read full with pretentious metabusllhit.
Harry's story is even easy to empathize with, since you as a Homestuck Reader what you wanted most is for John to have a happy life after the comic ended, so it hurts for you to see how John's marriage turned out to be unsuccessful for a decade, in the same way that it hurts to Harry that his father wasn't there with his mother in the house all those years and only now John begins to reconnect with his family, something which You as a reader and Harry hope will happen.