This release does not replace 2.9.4, it's simply a different flavor (the plumbing has been replaced with .NET generics). There were a few minor bug fixes that are included in the 2.9.4g release that are not avaliable for the 2.9.4 release, there are also a few API changes.
These are the official releases that have been fully tested by the Lucene.Net community. The binary library can also easily be incorporated into your applications using the NuGet Package Manager.