The big difference between Scotch
and Irish single malt whisky
is the distilling
phase which is made twice with scotch and three times with Irish. This gives each other special taste and noticeable lightness with Irish one.
Also the way how malts are dried is different. Scotch is dried with smoke which logically gives the usual scotch aroma to whisky. Irish is dried with pure air and therefore there is not any kind of smoke flavour.