Apart from major architectural differences, OBIEE 11g has several new features that were not available in 10g.
Some of the key features include:
Supports creating hierarchy objects in Subject Area
Export to xml or export to tab delimited/ and power point
11g lets variable have multiple values
11g RPD cannot be without a password
11g supports ragged hierarchies
Column selector in 11g can be defined on multiple columns, compared to just one column in 10g.
This video demonstrates the difference between OBIEE 11g and 10g in Oracle: