Is it 'ok' to solder an IC's thermal pad directly to a ground plane?
In case you use some professional reflow process, it is safe and good to design PCB as you do. I would even consider adding two "thermal vias" to other ground planes, if they are available.

You can even skip thermal reliefs on capacitors, they also solder very reliably on professional reflow equipment.

However, repairing of this PCB (to remove the IC and to solder it back) would be almost impossible without really good tools.

Another suggestion is to increase the width of connections between pins of IC and large ceramic capacitor on the right side: use fills instead of wires.