Decent enough for breakfast/brunch and the location can't be beat.
However, all the servers seem to be disinterested teens, and the frozen pub grub that gets served for lunch/dinner is not very appetizing.
Drivers beware - the parking lot next to the Grenadier is perpetually jammed in summer. On our last visit to High Park we spent 12 minutes driving there and 20 minutes cruising for parking. I suppose it was divine justice for not taking the TTC over.