This is my forum http://www.404forum.com/ I have recently moved my forum from vbulletin to Xenforo. My forum category is Webmaster, hopefully I can get some feedbacks on it's looks or how to improve my site.
Quite close to stock, so nice and quick, easy on the eye, easy to move around and not cluttered.
So picking up on the negatives and just opinions here...
I had trouble reading your logo, the font is terrible Maybe use a clearer font, or bigger lettering? the R U and M sort of all merge together.
The cookie message has a lot of space in it because the notice size is the same as your welcome message:
My suggestion would be, if you really need a cookie notice, to combine it with your welcome message so it's all in one notice. You see at the moment, as well as seeing lots of white space, you don't see your welcome message the moment you land. I'd argue your welcome message is more important out of the two. I actually prefer the add-on that brings up the welcome message in an overlay (with an X to remove it) because then it does not push your key content down.
Also with your welcome message, I'd move away from the "You are a guest" stuff (which is self evident) as the intro and actually say something about your forum. What is it about? Telling someone they're a guest and can't do things will not motivate them to join. Selling them a warm, welcoming community that's about a subject they're interested in would be a better way. I can't see anything at all that resembles and easy to find "About us" page.
The adverts in your sidebar are bigger than the sidebar on my screen and break out to the right.
The node icons are default and the blue does not go with your colour scheme. If you want to keep those graphics just run them through an image editor and change the hue to match (or de-saturate to a neutral grey).
In a nutshell you don't need to do a lot to make a nice change - better guest welcoming and a clearer logo IMO.