The God of the Old Testament made his presence directly and unambiguously known in many people's lives. He spoke directly to various Biblical figures, sent angels to speak on His behalf to various others. He was a very hands-on God. And while He changed His interaction significantly in the New Testament (sending Himself in the form of His son to directly interact with people), he was still very hands-on. But for the last two thousand years His approach has been decidedly hands-off. Now admittedly it depends somewhat on which faith or at least sect you subscribe to. There are Christian sects who believe in the visitations of other prophets, visitations of angels, and miracles, but even among these groups I think it's fair to say that fellow parishioners would look askance at any one arriving Sunday morning claiming a previous night's visitation by an angel bearing a great revelation. Something changed in God's interaction with us, or perhaps in our interaction with God. In either case I find the change hard to reconcile, and belief discouraged as a result.