Unfortunately, it appears that Google has recently retired the ability to turn off 3D imagery within Google Maps. They tout the ability to switch between the 2D and 3D views as their key feature in Google Maps, so they don't seem to be keen on disabling it.
That said, there are still a few options you can use to minimize the complexity of the 3D imagery. For one, you can adjust the quality of the 3D terrain: go to the settings menu and select the depth of detail you'd like to see (which influences how much data is loaded and displayed). Alternatively, you can also choose to display only folders containing imagery, which minimizes the amount of detail supplied by the 3D view.
Regrettably, it seems that there is no straightforward way to turn off 3D in Google Maps anymore. But hopefully these tips can help offset the overbearing complexity of the 3D display.