Sharepoint 2010 content editor is better than sharepoint2007 but it's lacking lots of functionality.
Is it possible to "substitute" standard rich text editor with something like Telerik Rad editor?
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You can use the Telerik RadEditor for SharePoint. You can download a trial version - to play around with it. Since I have experience with that control, I can tell you that this RTE also has his shortcomings. A perfect RTE does not exist.
You can create a custom field type inheriting SPFieldMultiLineText can use any third party RTE as field rendering control.
Normally, the third party RTE controls works with File System context. For contextual operations like 'upload file', 'add hyperlink of a page' etc , You may need to code a custom SharePoint context provider like Telerik Rad Editor does.