To have a better performance would be nice to cancel report rendering automatically or manually. 
If I am asking for a big report and after I change parameters and request new report, the previous request is still in progress and it is not going to be cancelled. Therefore I see high memory consumption on continuously refreshing a reports with a big data and after some time I see complete slow down of the Reporting Service and of course slow down of the server itself. The memory in this case is not released and Reporting Service crashes sometimes.

When exporting a long report with ContinuousPaper = true in Word format, the output document has text cut.

Based on the limitation explained in the Pagination section in Design Considerations for Word Rendering article of our documentation, Word supports maximum page size of 22 inches wide and 22 inches high. If the page is higher than 22 inches, some data may not be displayed in Print Layout view. So, in Word, a long document couldn't be rendered.

At least, this property could be avoided when printed in Word format.

Feature Request - Show email sent / error notification using the report viewers built-in notification system. 

It would be nice to have an option to have a message shown when the email with the report is sent or if there was an error sending.
Right now when you hit email and send the user does not know if it was successful or not. Being async is nice but I have noticed that it could take a few seconds to complete and if the user navigates away from the report viewer during this time the report has the possibility of not sending. Either way right now the user has no definitive method of knowing if the email was sent or not.

 

As a developer
I would like to have a built-in support for rendering various gauges in the report content
So that I can represent numeric values in a visually appealing way.

It would be extremely useful to have a Crosstab export the entire hierarchy as groups in Excel. SQL Reporting Services does this when exporting a report created there. I realize that this would mean generating the entire dataset prior to the export in order to expand all the data, but as I said, SSRS does this without a noticeable performance delay.

I am using the standalone report designer with an ObjectDataSource that returns ExpandoObject. I did create some new ExpandoObject objects and set property values as suggested in https://www.telerik.com/support/kb/reporting/details/how-to-use-objectdatasource-with-expandoobject. The problem I have that the dynamic properties of ExpandoObject are now showing in the data explorer.

StackTrace of the error:

 System.NullReferenceException: Object reference not set to an instance of an object.
   at System.Collections.Generic.Dictionary`2.TryInsert(TKey key, TValue value, InsertionBehavior behavior)
   at Telerik.Reporting.Interfaces.LocalizationContext.GetString(String resx, String key)
   at Telerik.Reporting.SRDescriptionAttribute.get_Description()
   at Telerik.Reporting.Expressions.EnumContextManager.GetItem(Type enumType)
   at Telerik.Reporting.Processing.ReportExpressionContext.RegisterAllReportingEnums()
   at Telerik.Reporting.Processing.ReportExpressionContext..ctor(Type reportType, AssemblyRefManager assemblyRefManager)   at Telerik.Reporting.Processing.ReportParametersManager`1.CreateExpressionContext(Report report, IList`1 runtimeParameters, AssemblyRefManager references)
   at Telerik.Reporting.Processing.ReportParametersManager`1..ctor(Report definitionReport, IEnumerable`1 definitionParameters, IDictionary`2 reportSourceParameters, IDataProviderContext dataProviderContext, AssemblyRefManager references)
   at Telerik.Reporting.Processing.DocumentParametersManager`1.CreateManager(Report definition, IDataProviderContext dataProviderContext, IParameterValueParser parameterValueParser, IDictionary`2 rsParameters, AssemblyRefManager references)   at Telerik.Reporting.Processing.DocumentParametersManager`1.CreateManagers(IProcessingContext context, IParameterValueParser parameterValueParser)
   at Telerik.Reporting.Processing.DocumentParametersManager`1..ctor(ResolvedReportDocument resolvedReports, IProcessingContext processingContext, IParameterValueParser parameterValueParser)
   at Telerik.Reporting.Processing.ReportProcessor.ProcessReportSource(ReportSource reportSource, IRenderingContext context)
   --- End of inner exception stack trace ---
   at Telerik.Reporting.Processing.ReportProcessor.ProcessReportSource(ReportSource reportSource, IRenderingContext context)
   at Telerik.Reporting.Processing.ReportProcessor.ProcessReportSource(ReportSource reportSource, Hashtable deviceInfo, IRenderingContext context)
   at Telerik.Reporting.Processing.ReportProcessor.ProcessAndRender(String format, ReportSource reportSource, Hashtable deviceInfo, IRenderingContext renderingContext, CreateStream createStreamCallback)
   at Telerik.Reporting.Processing.ReportProcessor.ProcessAndRenderStateless(String format, ReportSource reportSource, Hashtable deviceInfo, IRenderingContext renderingContext, CreateStream createStreamCallback)
   at Telerik.Reporting.Processing.ReportProcessor.RenderReport(String format, ReportSource reportSource, Hashtable deviceInfo, CreateStream createStreamCallback, String& documentName)