I'll just chime in by saying that while this is nice, it's generally best to put a user right into the site. Having a splash screen serves no real purpose and is more annoying than anything. I assume that if I clicked on "enter" I would go to the actual home page-so why did I have to click through another screen first? (keep in mind these comments aren't directed at you in particular MI5,

these are just general comments for everyone).
Best to just start there and instantly have the navigation available and let me get right to what I want to see.
But MI5, I understand that this was just an off-the-cuff idea, so I offer this as food for thought as you develop your site more. For now be proud of the start you've made-looks good! Don't be afraid to have some fun-I was thinking that you could have those pictures serve as navigation buttons with the addition of a bit of text. That would be cool-maybe they could even change as you moused over them (or fade or something)?
I'm anxious to see where you go next! :}
Tim