SUMPRODUCT first N even rows in a column (with criteria) then AVERAGE

the average of the first N (example 3) movies watched is now working

using an ArrayFormula

=ArrayFormula(AVERAGE(IF(ROW($D$2:$D$20)=SMALL(IF($D$2:$D$20="Complete",ROW($D$2:$D$20)),{1,2,3}),$C$2:$C$20)))

if you want to change the amount, for example the first 4 movies, then you need to change the code a follows:

{1,2,3,4}

if you want the LAST 3 movies watched, then change SMALL to LARGE:

=ArrayFormula(AVERAGE(IF(ROW($D$2:$D$20)=LARGE(IF($D$2:$D$20="Complete",ROW($D$2:$D$20)),{1,2,3}),$C$2:$C$20)))