Gamasutra - Turn-Based vs Real-Time
Electronic Arts designer Soren johnson discusses in this article the decisions that go into whether or not to make a turn-based or real-time game. It takes a look at the pros and cons of both styles of play:
At their core, turn-based and real-time games play to different strengths. One example is the question of whether an experience should be deterministic or chaotic. With the former, success often depends on knowing exactly what the results of one's actions will be; in Puzzle Quest, for example, the player needs to know that when a row of four skulls disappears, the other pieces will fall in a specific way so that a new column of consecutive red gems might form.
Just because some luck elements are involved - such as the unknown new pieces which fall from the top - doesn't mean that the player isn't mapping out an exact series of events in her head. This sequential gameplay is one of the core strengths of turn-based games. On the other hand, chaotic, unpredictable gameplay is a strength of real-time games.
When players first spot a heavy-medic combo in Team Fortress 2, they know that they are probably in trouble, but the sequence of events to follow is so varied that players know it's impossible to overanalyze the situation. A sniper could kill the medic. An explosion might knock the heavy off a platform. A spy might sneak up behind them. An event on the other side of the map might encourage one side to simply abandon the area.
Real-time games support chaotic gameplay best because, with the added pressure of a shared clock, players are not able to reduce each situation down to a repeatable series of moves and counter-moves.