There's some shadow inconstincy around the portal, note on the outside the shaodws are falling on the left side but the inner rim also has shadow on this side, whereas it would really be on the right inner rim. (Does that make sence? Lol, its quite late.)

This Antiqua again?

cool idea the whole background should be less saturated and you already know about the shadow

I like it, but to me the angles don't match up. I think it would be more effective with a more face-on portal. To sharpen both photoimages consistently would make it more visually effective too. I like the idea though!