Exactly what I thought! It definitely wasn't sweet enough, & this is coming from someone who doesn't
like things too sweet and almost always reduces the sugar in recipes! I think semi-sweet chocolate would have worked out better, plus a little more sugar. I added a touch more brown sugar in the topping, and it still wasn't quite enough. I rarely top cakes with powdered sugar, but this definitely needed it, and it helped a lot. I assume the glaze would have helped also, but I'm really not a glaze person - I usually find them too sweet.
If you want an outstanding recipe, let me know, and I'll post one of my favorites: CHOCOLATE SWIRL SOUR CREAM COFFEE CAKE from Godiva.