Not enough obscure and groovy stuff.
selected aspects (rated from ----- to +++++)
(note: I'm not rating everything or trying to break the flash up into constituent parts. Just giving you an idea of how good/bad I consider the points I mention.)
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+++: Most of the illusions you showed were fairly interesting.
+++: The new duck/rabbit was specially cool and worked really well just as an aesthetically pleasing graphic.
---: lack of 'work' done by you.
---: I've seen some illusions better than some of these, which you should have included, had your search been more thorough.
---: I had seen most of the illusions before. C'mon, everyone's seen the 2/3 prong fork...
----: Apart from the new duck/rabbit, there weren't any decent ones that were new to me.
---: your 'next' button has a terrible hitbox, it seems. Learn to make better buttons. Make a rectangle covering the whole graphic in the hitbox frame.
-: no 'replay' button at end.
-: no 'previous' button.
overall
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Minimal effort from you. It looks like you didn't even really search thoroughly enough to find quality stuff to be new to lovers of optical illusions (who would be the target audience for this, surely).
Considering the buttons were your main work here, the lousy hitboxes were almost unforgivable.
But I did enjoy seeing a few of these again and the new rabbit/duck is cool.