Simplify $A'B'C'D' + A'B'CD' + A'BCD' + ABCD' + AB'CD'$

It looks great. The one improvement that could be made is that the $C'$ is redundant, owing to an identity:

$$ZY'+Y=Z+Y$$

You can deduce this using the absorbtion law $ZY+Y=Y$, and the complementary law $Y+Y'=1$.

Intuitively, when adding part of $Z$ outside of $C$ to $C$, you may as well add all of $Z$ to $C$, because the part already inside $C$ will be abosorbed anyway.