Treestands are, without a doubt, fantastic hunting tools. They help get you above a deer's nose and eyes, and today's models are comfortable enough for all-day vigils.
Don't make the mistake of assuming that if you can't set up a treestand that you can't set up on a deer. The key to successful deer hunting is setting up in a location that you can get to undetected, and where the deer will be vulnerable. Sometimes such locations won’t have climbable trees, or even any trees at all.
Always set up downwind of where you expect to see the deer, and always keep cover between you and the deer so you can draw a bow or raise your gun. You might have to settle for several small shooting openings in order to remain concealed, but that is better than being too exposed.
Consider a ground blind, and also think about using the seat portion of your treestand near ground level if there are trees that aren't climbable.
The most important thing is to not become so dependent on your treestand that you overlook the best hunting sites.