Object-Orientation
There are a number of things that I look for in assessing if code has been written in an object-oriented way or in a procedural way - I've got a document somewhere that I wrote at a previous job, but this brief piece about "getters" by Martin Fowler is well worth reading.
Fowler assumes a fair amount of prior knowledge in his writing. For example, for this piece to make sense you need to know that "getters" is a term used for methods on Java classes that simply expose a field on the object.