Summary: My conclusion for excel services is that it's a suitable candidate when you need excel like capabilities over static data. It's a nice candidate for what-if analysis. If you intend to use it in the way you use SSRS with OLTP sources, Excel Services is definitely NOT the right choice. It's a good candidate for context-sensitive non-parameterized data, which is mostly the nature of data in OLAP sources having structures like dimensions and hierarchies. It's definitely not the right choice where you need to display data dynamically, real-time, and based on conditional parameterized querying mechanism.