His story concepts are generally good. SotN could have had a really amazing story if it were, say, a RPG. The whole family thing going on in that one was interesting and had a nice sense of melancholy to it.
The concept behind the Sorrow games is an interesting one too, and the initial plot twist that Soma is Dracula was actually pretty rad. I agree with the general consensus that the games could have ended better though. (Alucard killing Soma, Soma going nuts and killing everyone, etc.)
Lament of Innocence had something resembling a fleshed-out story and it was definitely enjoyable. It really enhanced the brooding mood and general experience. I'll take my Castlevanias with a dash of tragedy, please.
So yeah, generally he does a good job with the writing considering that these are action games. His one misstep was the disgusting Saturday morning cartoon vibe of Portrait, but I'm guessing that was intentional given that he was trying to market the game to a younger demographic. The man is trying to keep 2D games alive, here. If he felt he had to cater to children once to get more sales so that he could keep the series alive, I respect his decision even if it wasn't quite my favorite entry in the series.
And for people who complain that the series is stale, consider that IGA redesigns the game mechanics for almost every new installment. There are dozens of million-selling franchises out there that just release sequel after sequel with little but the number at the end of the title changed. (Gimme all dem Halos...)
And finally, he's always funny and courteous in interviews. He speaks about games in a way that I really appreciate because no other game designer still grasps the stuff that made games so great in the 90's. So yeah, I like IGA. He's an all-around rad guy.