I like that it allows you to use XML data for your reports in addition to standard SQL Server stored procedures/functions - this makes our development life easier as we can make changes without having to have someone who knows how Excel works with these formats.
The product has been around forever but still lacks some of the newer features offered by more modern products out there today (e.g., X++). There are better alternatives now so if you're looking at using something from Microsoft then go through their list here to see what they offer:-) We were trying to integrate an existing application into our new ERP system which was built mainly in C#/.Net Framework 4+.