When the gate valve is closed, it leaks at the stem and water still flows to the house. When it is open everything appears to be operating properly. The stem on the gate valve also appears to be sitting at an angle.

Every device has its problems. The water leaking at the stem should not be a problem if you tighten the nut through which the stem extends. If it will not tighten easily, it needs some additional packing which can be purchased at a hardware store. One of the problems inherent in gate valves is that the do not stop all water flow when closed. The angle of the stem should not make a difference if I understand what you to mean that the stem does not wobble when the handle is turned.