I cannot compare stats from the inventory... there is some compare feature from the shop but not from whatever is already in my inventory. Or Am I missing something ?
Currently the compare feature appears below the item you are looking at as a +/- attack rating (power level related) and +/- offence rating (dps) - There isn't a clear comparison implemented yet like other games.
Just found out by just left clicking on the object... It is not a mouse over :)