I think the Gallium driver for older Intel graphics is a bit
undercooked, and should not be considered a silver bullet (stable)
yet. I've been experiencing issues with WineD3D, like flickering, bad
performance and application crashing that I didn't have before. Wine
Nine did not help my situation.

When I've curiously tried these drivers on another distro before (this
was year or two ago, when this driver was experimental), I was able to
use MESA_LOADER_DRIVER_OVERRIDE=i965, to fall back to the legacy
driver. However this isn't possible on Debian:

I've tried 'apt-file search i965_dri.so', but it gave me no result. I
think this driver should be shipped with Debian, and perhaps (?) even
be preferred over Gallium for Gen 5 and probably Gen 4. The Gallium
driver just didn't have the years upon years of fixings that the i965
driver had.

I suspect i965 is part of mesa-amber now.

For those interested in a temporary, botched, solution, here is a
script (run as root):
#!/usr/bin/env bash
set -e
mkdir -p "/tmp/i965"
mkdir -p "/usr/lib/i386-linux-gnu"
mkdir -p "/usr/lib/x86_64-linux-gnu"
curl "http://ftp.us.debian.org/debian/pool/main/m/mesa/libgl1-mesa-dri_20.3.5-1_i386.deb"
| dpkg-deb -x - "/tmp/i965"
cp "/tmp/i965/usr/lib/i386-linux-gnu/dri/i915_dri.so"
"/usr/lib/i386-linux-gnu/dri/i965_dri.so"
curl "http://ftp.us.debian.org/debian/pool/main/m/mesa/libgl1-mesa-dri_20.3.5-1_amd64.deb"
| dpkg-deb -x - "/tmp/i965"
cp "/tmp/i965/usr/lib/x86_64-linux-gnu/dri/i915_dri.so"
"/usr/lib/x86_64-linux-gnu/dri/i965_dri.so"
rm -rf "/tmp/i965"

This will install the old i915 driver, with i965 support. To use it,
do 'MESA_LOADER_DRIVER_OVERRIDE=i965 your-application'.