ResizeBuffers works but your general observation is correct: DXGI is simpler if you're using it at the most basic level (starting up in a single mode and never switching from that mode aside from using Alt-Enter to toggle fullscreen/windowed, letting DXGI handle the toggle) but as soon as you try to implement your own mode switching, with support for different resolutions, refresh rates and windowed versus fullscreen, it becomes significantly more complex than the old way.
As a general rule, the sequence that works looks like this:
If going from fullscreen to windowed, call SetFullscreenState (FALSE, NULL), then call ResizeTarget.
If going from windowed to fullscreen, call ResizeTarget, then call SetFullscreenState (TRUE, NULL).
Otherwise just call ResizeTarget.
Wait for a WM_SIZE message to come in (the OS will generate this automatically in response to the ResizeTarget call).
Call ClearState, OMSetRenderTargets (NULL), and release your current RenderTargets to ensure you've cleared any outstanding references on your buffers.
Call ResizeBuffers.
Recreate anything that needs to be recreated (typically your backbuffer's RTV, your depth/stencil texture and it's DSV, and any other render targets you're using)
Generally I don't respond immedately to events as they happen when doing this; I've found that doing so is almost 100% guaranteed to get things happening in the wrong sequence and mess up badly. Problems I've observed include back buffers not being sized correctly for the window, the taskbar size interfering with fullscreen modes, etc. Instead I just set a flag on my video state, and at the start of the next frame I check for this flag and respond to it there. If the response requires any kind of follow-up, I set another flag and defer again to the following frame. If all flags are clear, I draw the frame, otherwise I skip drawing it.
It's also important to use MakeWindowAssociation with DXGI_MWA_NO_WINDOW_CHANGES | DXGI_MWA_NO_ALT_ENTER, using a DXGI Factory obtained via SwapChain->GetParent, otherwise DXGI may kick in and decide to do it's own thing (instead of what you want it to do) at any point during this process.
