Frankly speaking,
1) the mixed usage of subquery in SELECT clause and join could be confusing. Even if the syntax is correct and there are no problem to parse the query, are you sure the result is what you want?
If the subquery's result has more than one rows, the final result would depend on what relational database you use. In some databases, it is legal but the final result might not be what you mean to have. In some other databases, it could be illegal. Make sure to write queries that are legal in all the commonly used databases, unless a feature specific to your database is of great help either semantically or in performance.
For this query, join is the better choice.
2). Looking at the query only, both column "documentation_level_desc" and column "SPECIAL_FEATURE_CODE" could be problematic. Could you give the table definitions?
3). I am not sure if you are aware of in what order the different clauses are evaluated. It might help to figure out the query, and in turn, write better queries in general if you study it a little. It will give you an idea what the execution plan will look like.
