English is really a fairly ugly language. It's got a lot of exceptions and violations of the rules, not to mention a rapidly evolving vernacular and colloquial expressions. I've heard from several friends who have other languages as their first that English is extremely hard to learn because of all the nuances and exceptions, then even harder to become functional / fluent in due to regional dialects and colloquialisms.
On this subject of "awful" = "awe" + "full" I think the etymology is pretty straightforward. One can be in awe of something that's terrible, bad or rotten just as much as they can be in awe of something wondrous, positive or great. It's interesting that the word "awful" doesn't capture this duality and only goes to the negative. It's even more interesting (and confusing) that "awesome" (used for positive things) breaks down to mean "some" + "awe", so the language implies that negative things ("awe" + "full") carry more weight or have more impact than positive ones ("awe" + "some").
English is a mess, it really is.
