I'm loving the look of the new Quintessential line, although I think the Fighter image needs a frame as per the Wizard image. And I would leave off the company logos on the front, very distracting.
Overall, I like most of the Mongoose covers with a full colour image of the subject and line-logo heading.
For me, it's definitely the interior layout that let's the books down. Whole line spacing between paragraphs makes them look like early reader books. Justification of 'short' lines is criminal as is justification of headers. Breaking column width with pictures is another Mongoose habit which is OK as long as it doesn't force runaround text to be 3 words or less. Some of the header styles used are equally nasty and hard to read. Widows and orphans are liberally scattered and the table style is very average. Spacing needs to be used better, especially around a/ws and headers.
Page borders are usually fine as long as they are not too intrusive, nice when they incorporate the page number and chapter head.
I could go on, but those are my main Mongoose Bugbears. Hope that helps, Will.
Cheers
Sam
(Celebrating 25 years of employment as a Graphic Designer and Layout artist)