@Borkachev
You're mixing complexity with depth, or giving complexity too much weight in terms of depth.
Most of GTA's depth comes from its sandbox design, free roaming and the large playfield. Every GTA game is also quite accessible and simple - get a gun or a car and go on a rampage.
Pretty sure I addressed that. I said that hardcore games aren't necessarily deeper than casual games (although most are), they just get their depth from somewhere else -- their complexity.
And GTA is fairly accessible, which is part of the key to its success. But that's only half the formula to a casual game, and GTA has far too many game mechanics to be called casual.