abstruse — You can describe something as abstruse if you find it difficult to understand, especially when you think it could be explained more simply.
complex — Something that is complex has many different parts, and is therefore often difficult to understand.
complicated — If you say that something is complicated, you mean it has so many parts or aspects that it is difficult to understand or deal with.
difficult — not easily or readily done; requiring much labor, skill, or planning to be performed successfully; hard: a difficult job.
hard — not soft; solid and firm to the touch; unyielding to pressure and impenetrable or almost impenetrable.
intricate — having many interrelated parts or facets; entangled or involved: an intricate maze.
involved — very intricate or complex: an involved reply.
unclear — free from darkness, obscurity, or cloudiness; light: a clear day.
vague — not clearly or explicitly stated or expressed: vague promises.
aware — If you are aware of something, you know about it.
cluttered — filled with things or people in an untidy way
convoluted — If you describe a sentence, idea, or system as convoluted, you mean that it is complicated and difficult to understand.
decorated — (often initial capital letter) of pertaining to, or characteristic of the English gothic architecture of the late 13th through the late 14th centuries, characterized by curvilinear tracery, elaborate ornamental sculpture and vaulting, and refinement of stonecutting techniques.
embellished — Simple past tense and past participle of embellish.
exacting — Making great demands on one's skill, attention, or other resources.
intelligent — having good understanding or a high mental capacity; quick to comprehend, as persons or animals: an intelligent student.
jumbled — to mix in a confused mass; put or throw together without order: You've jumbled up all the cards.
mature — ripe, as fruit, or fully aged, as cheese or wine.
older — far advanced in the years of one's or its life: an old man; an old horse; an old tree.
ornate — elaborately or sumptuously adorned, often excessively or showily so: They bought an ornate Louis XIV sofa.
smart — having or showing quick intelligence or ready mental capability: a smart student.
