They made the wall way too thin. Jon and Ygritte looked over the lip on the North side, turned around, walked across a little path, and were at the Southern edge. Aren't there supposed to be tunnels and passages through the ice? 700 hundred feet tall and 12 feet wide: you'd expect it to be swaying back and forth. The wildlings could have just dug right through it. The climb up the wall was thrilling though. As an action sequence, it was more successful than you normally see in a television show.