The time to cast and the inability to defend themselves is the major drawback of sorcery. In this respect, RQII sorcerers are a lot like traditional wizards in other game systems, creating the need for the sorcerer to stand in the back and wave his hands around while the grunts take the initial assault.
Fortunately, there are a lot of spells that can do a lot in one CA, and also since RQII is a classless system, once the Sorcerer runs out of magic points, s/he is not instantly worthless.
Sorcerers can do some scary stuff, though. Multi-target teleports, wracks, diminishes, palsy, holdfasts, healings (good or bad depending on who is doing it).