Intellisense on DB objects, from inside Visual Studio is fantastic. I obviously didn't write that, but there's this great TSQL editor just sitting there doing nothing, because there was no solution for integrating the sql into your app.
Testing, I believe, is my strongest point. Your queries are tested every time you save the file, or you can test and regenerate all queries in your app via the tools menu ("Merde, someone changed my schema"), or you can run the bundled integration tests. If your queries don't run, or if the parameters or return schema change, your app doesn't compile.