Like Kitkun said. Rook is big, like, Big, it makes sense smaller things just get lost in it's shadow. Just played my first few games with Rook, and it was a powertrip. I didn't get as many kills as with Regulus or such, but just.. creeps get lost beneath Rook, they just die without Rook even noticing. I even accidentally killed a player with Hammer Slam, didn't even notice he was there (there were giants and such around).
I didn't really have any big problem with Rook's size though. If a player is hidden behind Rook when I target Hammer Slam, it will also hit.
Aside from Rook though, targetting smaller characters in a crowd is annoying. Especially having trouble targetting my own demigod is stupid, why can't I just target the big picture. Or even better, cast on self with a key modifier. It's not that bad if I can't target other demigods so easily, I imagine it might be hard to target somebody during battle in a crowd. But my own character?