I figured since its been like 4 days that it was probably too late to respond.. since you probably would've found your answers..
Anyways, the very first document you should closely look at is the " QuickStart Tutorial Guide (Word 2007 format) " found here:
http://quickstartengine.codeplex.com/Release/ProjectReleases.aspx?ReleaseId=21358
That doc is meant for .195 and later, so if your using an earlier version of the engine, take a look here:
http://quickstartengine.codeplex.com/Wiki/View.aspx?title=Getting%20Started%20Tutorial
It gives a good basic overview of the engine... and at the end of the doc it lists what the engine currently lacks.
The engine is far from being complete. It's limited to what it can do and missing a lot of features that you'd normally want within a game. However, it looks like its built well and made in a way to easily add new components to it. Its unforuniate that the engine has been in sort of a frozen state since Jan. and only LordIkon is really working on it whenever he gets around to working on it.
So can you make an FPS with this engine? Yes! But you're going to have to add a lot to the engine to make it work. Some things I'm looking into for my game is Animated models, AI, and other graphical goodies (i.e. water, skydomes, etc).
I've looked around and there's not really any other free (and GOOD) engines out there for XNA developement. The best engine is the one you make - since you understand what its doing at its core.
Here's a list of "release" milestones.. but as you can see from the list and when it was posted, its been about a year since.
http://quickstartengine.codeplex.com/Release/ProjectReleases.aspx?ReleaseId=8733
Click on the right side to view other "release" milestones for different versions of the engine. As you read through those lists, you can get a sense of what the engine is missing...
Don't expect those "releases" to come anytime soon. :*(
.ilarion