It is incorrect to ask whether or not free-will exists. A more direct form of the question can be formulated as "in a group of systems, can one system affect another system?"
This allows us to see the issue from a new perspective, which is almost an inverse perspective. Rather than considering "can I make a decision?" We can ask ourselves, "can someone else's decision have an effect within my life?"
To me, it becomes apparent that it does not matter whether or not external entities from myself have the capability of "choice-making." What is more important is if these external entities can have an effect on myself regardless of my own will. My experience tells me that yes, external entities can affect me regardless of my internal will. But am I entirely powerless to the outer world? No. It would be entirely logical to assume that if the external world can affect me, then I can affect the external world.
So a deeper question than "does free will exist?" might be "is my influence over the world derived from my will?"
It is indisputable that within the mind there is some aspect which we can label as "will." Will is that aspect of the mind which discriminates and desires. Will is the aspect of the mind which takes the perception of reality and urges reality to present itself differently. The aspect of human consciousness which we refer to as "Will" is the aspect which creates art, or sees suffering and produces acts of compassion to reduce suffering. This aspect of the mind exists, we can describe it, we can experience it, we can observe how it behaves.
Is "Will" free? Does the aspect of the mind which we call "Will" have the freedom to behave in any way it pleases? My argument is that freedom of will is not clear-cut. The mind can will anything it pleases. In the sense that we can desire anything we want, we do have free will. However, desire does not necessarily create reality. In fact, most desires do not have much effect, if any, on the world outside of the mind which is experiencing desire. The Will of the mind depends upon the capability of the body which is controlled by the mind. If the body does not have the capability to manifest itself as the will's desire, then no amount of willpower can change the physical incapability. In other words, Will-power is a force within our existence, but it is a force which competes with other forces. As a naturalistic pantheist, I see Willpower as a sort of "meta-force" which is a special type of combination of elementary natural forces in the universe.
By seeing that Will is not a basic aspect of the universe, but actually a complex aspect, we can begin to appreciate how the "question of free will" is misformulated. Within every Will is a combination of forces which are all attempting to create a particular outcome. Outside of every Will is an entire world of many other Wills and many other forces which are attempting to create many other different outcomes. We can therefore think of Willpower as a probable range of outcomes resulting from the interaction of constituent forces within the body which is partially governed by Willpower. To further complicate matters, external forces acting upon an individual's Will can make impossible the expression of certain probable outcomes.
To try and succinctly describe this nature of the world which I am postulating we live in, I would say that we have free will, but our free will has limits which are subject to a nearly infinite or probably infinite number of external free wills. Unfortunately, I am ignorant to possible ways of mathematically expressing this system which I believe we are living within. My gut tells me that if we were to calculate the "amount" of free will we have, we would find that we basically have a small effect on the world, and the power of our will is most simply described as random.
So do your decisions matter? Well, yes. Actually, every decision you make could potentially change everything, but realistically, most decisions have basically no effect. In a world with "local free-will" we have infinite responsibility, yet we are infinitely insignificant. Every decision could turn out to be the most important decision ever, and simultaneously every decision could turn out to never matter at all.
Finally, what of God? I believe that God has created this system for us to have the opportunity to express free-will, so that eventually we may return to a perfect universe without free-will. I believe that on a very fundamental level, free-will is an essential element to existence itself. Without free-will, there is no consciousness, because no matter what future comes, no decisions can be made, therefore the entire universe is stationary. For a universe to have any activity, I can only imagine three possibilities. 1) A completely random system, where interactions are meaningless because every possible interaction is guaranteed to happen. 2) A completely logical system, where every interaction is meaningless because it is predetermined. or 3) A conscious system where interactions are meaningful because there is no predictable outcome, but not every outcome can happen.