Barrapunto

One other type of unreadable code I often encounter is over-engineered object-oriented (OO) systems. Software of this type uses deep inheritance hierarchies and multiple levels of delegation for no immediately apparent reason (other than to show off the programmer's mastery of OO concepts). When such systems lack design documentation--and, unfortunately, this is often the case--they can be more difficult to understand than any old-style spaghetti code. [...] Think of it as a sequence of goto's with the target being stored in a variable.
I get a lot more frustrated with code that's gratuitously over-engineered than with inherently complex code.