Phone case is a definite in my opinion too, feels nice naked yet a bit too vulnerable left in that state.
Had a couple of issues with my 650 but they could be related to the reason mine was sent back for exchange, in the cold my display was rendered useless and once it went off (my doing or its own) could not get it to come back on until phone was brought inside and warmed up. Before that came to light we were experiencing an abnormal amount of screen flash/flicker similar to what was being reported/seen on my 830, was surprised the 650 had this ailment too although much worse. Glance Screen also had this unusual "twitch" that seemed a tad out of the ordinary, can't quite pinpoint but was noticeable on many occasions.
Other than that I thought it was a decent phone even for the $200 asking price, definitely no powerhouse with some limitations but the biggest crippler IMO is the OS. Hopefully Microsoft fixes what needs to be fixed before the phone becomes nothing more than a feather in one's cap... Too light as a paperweight LOL.