Change that increases functionality/usability is good. Change that reduces it is bad. The font makes no difference and no longer showing the threads with new posts reduces it.
Yes, they are no longer bold by design. Fonts also changed to closer match Mobile theme.
I would personally request that the 'bold for unread' is brought back into play. It's hard to know which threads you've read if reading new posts out of chronological order. It'll result in a lot more 'search for new posts' than just pressing backup and then clicking into the next thread.
Fonts being different is well explained though
I assume you've taken into account font rendering in different browsers when making this assessment.