The new design is sexy-ish, but I think readability suffers because:

1. the contrast is too low, for example that blue colour of links on white background is too light, hurts my eyes

2. the font-size is too small, especially in combination with the poor contrast. 14px is too small on today's desktops, should be 16px ... better yet, it should be left at 100% as that scales better. On the other hand I like the usage of Open Sans, it's a readable font and ensures availability on all OSes

3. some pages are too slow to load. MDN is a great reference and decreasing latency should be a priority.