I like the overall feeling to the poster, it's jolly and optimistic because of the large yellow area. I believe the font size used for the memberships is a bit too small but all in all it's a nice, simple and straight-forward poster. So i believe it reached its purpose.
The colors, text and imagery do a good job of carrying the theme of the convention. This looks different, and fun!
Some things that might be touched up:
1. I think the information could use a little reorganization. The dates and location of the con could be given more priority I think. Perhaps moving them up to where the membership info is now, but making them larger and more readable. It is important info.
2: The leftmost (to our eyes) arm of the jester cap appears to be running into the planet she is so deftly spinning.
Other than that, I really like the poster, and especially that ampersand! Good work!
but I would like to suggest a few things here[ these are my personal opinions]
1.the bottom of the poster
"dealers room. Art Show" n all
it'd be nice if you could invert them so that they are readable
i know that you'd trying to maintain the effect of text acting as a border around it but readability is a key feature when it comes to a poster
2. the title of the poster
"A weekend of science fiction and fantasy" is taking up too much space, not that its bad or something but its making the whole poster look cramped. try freeing some space and distributing the contents evenly.
I agree that the information could be organized a bit more efficiently, for example the pricing lives all by itself in an odd place, maybe that information needs to be with the date.
Also, I'm a bit bothered by the type as a border element; you're trapping uncomfortable neg spaces in the corners for one. Also, you might try setting that type in all caps so that it has cleaner edges, like a linear border.
I also agree with the comment that it feels cramped. Don't be afraid of neg space, as long as it flows and isnt trapped. The writer guests/artist guests lines get a bit too close to the border for comfort, and the place and dates is so similar in size to the border type that it is hard to differentiate the two.
I like the idea..but it looks broken in 3 pieces, maybe you could try with an "horizontal" composition.. and try to integrate the title "FoolsCap" with the illustration".
Also, be careful with the yellow of the planet, it gets a little bit mixed with the background and remember that usually the titles are in the header.. so "a week of sci-fiction & fantasy" is the sub-title(actually it look like anothe tittle).