I've a colleague who is an access guru, and he will probably disagree, but here is what I think..
Ease of use - you don't have to be a programmer to use CR. You can get started on simple stuff very easily.
Security - Cr is read only, so won't damage your database.
Formulas - far more functions and complexity of calculations, you can even add your own as User Function Libraries.
Formatting - more format options, better conditional formatting, better grouping and more group options.
Databases - yes you can link tables into access, but Cr has a wide range of other data sources.
Performance - Even with linked tables, processing AR takes place in Access, Cr talks SQL directly to the database and performs a lot faster. It can also handle larger volumes of data and do thinks like grouping on server.
Integration - If you are developing in VB, .NET or another language you can integrate your reports within your app including dynamic viewers.
Abstraction - In CR10, you can use Business Views to abstract parts of your database, select Live/Test Db's at run time, and secure sensitive content.
The brick walls are a lot closer in MS Access. When you hit them it is hard to get past them. With CR they are a lot further away and there are many ways over these technical hurdles.
Editor and Publisher of Crystal Clear