I like the overall look of the site as it loads, so the first impression is good.
There are/is a layout issue with the design on both the sides and the footer (I use IE6).
There seems to be a lot of white space towards the bottom right of the homepage, with so many magazines listed on your site you should be able to find some content for that space.
I'm not a great fan of sites where every time you go back to the homepage ALL the content has changed... two things caught my eye, I clicked one and when I returned to the homepage - the other was gone.
Your buttons need to have the corners colured to fit in with the page colours properly, they look nice with the curves.
I'd really like to see how many issues you get, right there at the top, eg:
Skirmish Magazine - from £31.00 doesn't tell me what I'm getting.
Skirmish Magazine - from £31.00 (12 Issues), would do the trick.
I'd like to see your contact page more apparent, with some contact details (even a PO Box).
Personally I would scrap the category page and add all the categories straight down the side of EVERY page (or in the footer)... you could even make it into a drop menu (not that I would advise that)
All in all it's a good looking site and appears to do what it says on the tin
hope this helps...how's your traffic to the site?
regards
James.