Today I encountered a weird issue, the classic Visual Web Part template was gone in Visual Studio 2012. When I created a Visual WebPart, a webpart was created with a generated .g.cs file, like the sandboxed visual webparts. I am not exactly sure why it happened. According to the MSDN guide Creating Web Parts for SharePoint, the structure of Visual Webparts should be the same as in Visual Studio 2010. It could have happened after I installed the power tools.