What if it was extended to absorb both spells and effects?...
Granted that would seem, at first glance, to make it worse... However, since creature abilities are typically reusable, it would really end up meaning that the opponent would be forced to "sacrifice" a creature skill each turn in order to use offensive spells.
E.g. if the opponent had an owl's eye and a shockwave, they could use the owl's eye (which would get absorbed) so that the could then cast shockwave effectively.
Also, why not extend the effect from just creatures into any cards the owner has in play (e.g. creatures and permanents).
Again, if skills / abilities are absorbed as well, it just means that the opponent has to expend a (reusable) creature or permanent skill in order to open up use of a (one-shot) spell effect.
Putting a limit of 3 or so absorbs would definitely help balance it if this still seems too OP.
So something like:
"Absorb 1 spell or skill that targets a card you own per opponents turn.
Absorbs 3 effects."