Sorry I can't give an official critique, so I'll just list it here:
Firstly, the background- amazing. Astonishingly fantastic- I love that it shows the out-of-shape panels, the potato plant and behind-the-scenes parts of the facility. What I find most striking is the use of colour and light here- how it combines the classic portal colours without seeming cliched. The textures are brilliantly subtle. Secondly, the Excursion Funnel is wonderful- I love the style you've used, making it recognisable, but still unique to yourself, and how it blurs as it nears the edges of the art, enhancing the 3-D effect. Lastly, Wheatley. I can not express my awe in the colour, lines and light used here. Much like with your Excursion Funnel, he is immediately recognisable, but subtly different. Amazing. I am now off to watch your profile and favourite your Portal art.