The biggest criticism that I have seen growing over the recent years are the concerns over the energy being spent mining bitcoin, however as we know those numbers have been exaggerated just to try to get the young, which are environmental conscious, to not adopt bitcoin, however the biggest weakness for the average user is the confirmation speed and the fees, as even people like us sometimes have problems getting a confirmation when we want to move our coins, and we may have to refrain from sending any transaction at the time as the fees are higher than the amount of bitcoin we want to send.