"Lacking a Z-axis" is a very broad term. Do you mean as a gameplay mechanic (gameplay takes place on a flat plane) of visually (the game utilizes 3D models instead of 2D sprites)?
Over 90% of strategy and tactics games lacks a Z-axis that has any impact on the game, even the recent ones. Civ 5, Endless Space, Heroes of Might and Magic 6, to name only a few. RPGs frequently neglect to put it to any use as well, like with Dragon Age. On the other hand, there are plenty of old pre-3D games that used the Z-axis in their gameplay. The original XCOM springs to mind.