A popular argument these days in game design is whether it's better for games to be more complex or not. StarCraft 2 is a great examples of a game where this argument comes up frequently. StarCraft 2 met with much criticism upon release because fans of StarCraft 1 complained that StarCraft 2 lacked "depth."
In order to really understand the issue, first, we need to talk about what "depth" is.in terms of competitive games. I believe a fair definition of "depth" in this case is how much room the game allows for players to distinguish themselves in terms of skill as measured by success.
For example, a game like tic-tac-toe lacks depth because there is not much room to distinguish one player from another in terms of skill. The game doesn't have nearly enough possible states, so it can be played perfectly. The small number of possible states also means that the average player can follow this perfect line of play without much experience.
A game like chess has a lot more depth, because there are a huge number of possible board states, so it's nearly impossible for a human player to play perfectly. It's fair to say that the rules of the game are relatively simple by today's standards, though. A player can learn the rules of the game fairly quickly, and mechanical execution is trivially simple.
Competitive real time games like StarCraft 2 include the element of mechanical skill while still requiring strategic skill since they occur in real time. Mechanical skill introduces another layer of depth since it adds another dimension in which players can distinguish themselves in skill. In fact, the top professional players of these sorts of games tend to be young (15 to 20 years old) since they need to have quick reflexes and nimble hands.
StarCraft 2 was criticized upon release for removing certain mechanical skill requirements that existed in StarCraft 1. One example is unit production. In StarCraft 1, a player had to quickly cycle through all of his production buildings to order units to be produced. In StarCraft 2, a player could select all of his production buildings at the same time and the game would automatically distribute unit production among those buildings, removing the need to cycle through all the buildings one at a time. Players complained that this removed depth from the game.
It's pretty clear from our definition of depth that this design decision removed complexity and consequently some depth from the game. Players who were better at cycling through buildings to produce units while juggling all of the other game tasks were able to gain an advantage. But what these players forgot to ask themselves was whether this is good depth. Is this an interesting skill that people like to see? Should the winner of the match bet determined by who cycles through buildings better?
Removing this sort of complexity allows the winner to be determined by more interesting skills, such as strategic decision-making and actual micromanagement in combat. There is still clearly more than enough depth in the game for professional players to distinguish themselves in skill, as seen by the endless shifts in who the top players are. Players are continually developing new strategies and builds to counter the current top players.
Thus, Blizzard appears to have made the right choice. Complexity for the sake of complexity is not necessarily good depth.