I am pretty sure I have seen a word for someone who often misses small details, but it has slipped out of my mind. Any ideas?
I looked up "observant," the antonym at thesaurus.com and there seem to be no suitable adjectives without a negating prefix, but "unobservant" or "imperceptive" might fit.
The opposite of detail oriented is 'visionary', that is, if you want to focus on the positive connotations of someone that looks at the big picture. If you are looking to focus on the negatives, then you might want to go with careless or thoughtless. If you wanted a word that points out the negatives of someone with great attention to detail you could go with 'anal retentive'.