I felt movement at 16 weeks onward with anterior placenta, but all feeling has been off to the side. Once I hit around 27 weeks I was feeling (and seeing) bums, heads, shoulders etc rolling around under the skin.
My early experiences were like some one flicking a finger against me (like a popping) but not painful and from the inside. Usually at night whilst watching tv. Some movement felt a bit like a muscle spasm but in the area you'd expect the baby to be - if that makes sense.