These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Paranoia Fuel: A dead person's spirit can randomly possess you at any time and demand that you do all sorts of things. And if you refuse he can probably make your life a living hell, considering the fact that he's with you all the time. Sure, Sai is pretty nice, but imagine what it could have been with a nastier person.
Sai is probably the most unintentionally effeminate male characters in all of manga. His effeminacy is perfectly in line with the sensibility of Heian period nobility, but that doesn't make the experience of watching an adult man giggle like a schoolgirl any less jarring. In fact, the author had to correct the English translator(s?) when they used "she" to refer to him.
Touya Akira looks strangely girly too, with his jaw-length bob hairstyle and rather ambiguous clothes. There is lots of fan-art around which puts him girl's clothes. Akira's case isn't helped by the fact that he's voiced by a woman.
Wangst: After Hikaru realizes that Sai has disappeared, probably forever, he goes into a state of complete moping. He ignores his scheduled pro games (even vowing to quit Go altogether, even after coming so far), he ignores his friends, he ignores his family, he just locks all his emotions up and mopes.
What an Idiot / What the Hell, Hero?: There are several times when Hikaru rashly ignores Sai's advice and plays haphazardly, losing as a result. Akira even gets pissed off when he thinks Hikaru is doing this to spite him.
WTH, Costuming Department?: Akira's pink sweater-vest and lavender suit. His clothes were always a bit... unique, shall we call it, but this◊ was going too far for some people.