denser

heavy impenetrable opaque solid

close compact condensed crammed crowded heaped jam-packed jammed massed packed packed like sardines piled substantial thickset

clear easy soft understandable

open scattered sparse thin uncompressed

dull simple thick

blockheaded boorish doltish dumb fatheaded ignorant imbecilic impassive lethargic numskulled oafish obtuse phlegmatic slow-witted sluggish stolid torpid

intelligent smart

brainy clever