LOVE it! Fantastic work!

It's very very easy.

Step 1: Set up your viewport (either ortho or frustum, basically)
Step 2: Make sure depth testing is off.
Step 3: Draw all your 2D crap (if you're using ortho, just do it using X/Y coordinates, if you're using frustum, rotate it against the camera)
Step 4: Turn depth testing on.
Step 5: Draw all your 3D crap.

Getting stuff to line up just right can be a slightly difficulty but (especially if you're using ortho) it really isn't very hard at all.

it goes without saying that it's great, but

Final Countdown, omg...

apart from the fact that I don't like it, which is taste and subjective; why not something original ?
never heard of a game using a mainstream song as BG music... aside from MJ's Moonwalker obviously

mainstream music and video games - do not fit together

More like nothing :<

Well I'm fine with any game having AC/DC as BG music for example, but still... mainstream music in games, no no

I guess now by thinking of it, many racing games have mainstream music
but obviously they have much of it, and in good games you can actually select for every song if you ever want to hear it (NFS)