Can't say I'm a fan of the new style/layout.
Seems to be a lot of wasted space in certain views (yet it still doesn't scale that well on lower resultions for some reason), and it feels like there are less details available on any one view at any given time.
Going for the 'flat' or google design language is all well and good on a mobile, but on larger displays it's just a waste and looks bland. (the old theme may not have been snazzy, but it allowed for a forum that was very easy to navigate and read. With clear distinctions between posts. It was clear and effective, unlike a lot of other forums these days.
Almost seems like the colours are wasted out and making text harder to read/distinguish in places.
I'm sure under the hood there are numerous changes to help make the forum better, more efficient resource use etc. which is good and it does feel pretty quick.
Also, the edit post button really should be located on the right hand side of your post. It is not intuitive (or logical) to have it on the left beside the report button.