Not happy that:
- Wifi doesn't work, it connects and immediately disconnects
- Elevation reads about 30 m high
- Sensitive touch screen
On #1, are you successfully using automatic WiFi sync with other Garmin products; it may be one of several bugs that can be worked around (e.g. incompatible WiFi router channels); if you have a browse on the forum you might be able to solve that.
On #2, you know that you have to (regularly) calibrate barometric altimeters right? This can be done a number of ways, but I'm guessing the Edge 820 has continuous GPS-based calibration, you might want to check if that's turned on.