The 3D graphics is simple, but it has some strange magic that works on me. It is playful sandbox.
Personally I am missing some "challange" that will make me to think what poison to use or where to use it. For example some "friendly" animals that you don't want to hurt (Just to be safe - disclaimer: in real life do not harm ANY animal :-D ).
Poison combination mechanic can be fun concept, but currently it is too easy to unlock all combinations. Also now you create new poison by combining two same previous one - I think it would be more fun if the combinations was more "sophisticated" (Things like water + air = fog etc.) so it can provide some joy in discovering them.
Overall I think its nice groundwork with potential. And after all - in one week nice job!