Design wise its pretty but i have my gripes with it.
First and foremost, it looks like its made for smartphones. Things are oversimplified and for the most part not inutive.
As example is this navigation bubble which doesnt actually let you navigate anything, the header that looks like it would have dropdowns for more options but doesnt. Spoilers that dont highlight nor animate on hover to signify that they're clickable.
The color sheme is fancy but unfriendly to the eyes, particulary the white background of the posts area stands out there and hurts in the eyes, please use a less bright and intense color, a light grayish blue like on the current forum is much easier on the eyes.
On the profile pages where the about me begins, the dark gray background does magnify the effect of the white background in the main area. I get what you were going for design wise, but perhaps it would be better to gradually darken the outer background as you scroll down and instead keep the dark gray bar at the width of the active area. Also, fade the bar out when the user scrolls down and only fade it in when the user hovers near the top of the page - or make it less thick.
Moving on to the index page and more to the functionality side of things, i get the feel that the space is badly and inefficently used, it does look good and all, but userexperience should go before design. As suggestion, decrease the border between the invidual boards - currently you could fit two if not three lines of text there, too much. Again, a designed for mobile feel comes up - things are bigger than they should be.
Likewise on list of threads - decrease the distance between them. This continues further in the threads themselfes, 2 posts with oneliners fit just barely on my screen, altough here its mostly due the increased font size - decreasing the font size by one would help with the longer posts but one liners and short posts, especially those from users without signature have the issue of empty space.

Whats with these 2 cm of nothing? cut that off.
Similary with posts such as this:

The supporter heart should be next to the flag and the signature under the text, next to the avatar border thingy. Dont leave it sticking out like a sore thumb unless the text pushes it out.

More empty, unused, wasted space i have to scroll past, this should be almost half as thick. Same applies to the Pippi header on the index (but its far less worse here, it just needs to be a bit thinner, nothing as severe as half as thick) - from a users side its space you have to scroll past before you can do whatever you wanted to do. A nuisance in the long run.
Then of lastly and finally, theres features outright missing i understand its WIP but... Where are the maps on the profile? changing avatar? PMs? Where do i access the user control panel for changing settings? Where do i click to see the oldest unread post in a thread? Subscribing to threads? I could go on for ages - not even half the functionality is here.
...Pages? Even semi paigation where you just jump 20 posts or so would be A START.
Have a simple ticker under/above the navigation bubble that scrolls right by one page for every 20 post count. Replace the jump to first/last post of the bubble with jump 20 posts forward/backwards and let the ticker take care of the jump to first/last post. Make the post count pop up the jump to post, rather than linking the current post (its just more inutive), add post numbers to the posts themselfes to take care of the direct linking instead. Possibly fade the ticker, the current jump-to-bubble (yes keep it, accessibly is good) and any other bubbles you want to add out unless the user hovers on the bubble. Long story short: Make the navigation bubble actually let you navigate the thread rather than being a needlessy fancy post counter. Hell, i might just swish something together on photoshop to illustrate what im talking about here.
Make infinite scrolling preload 5 or so posts into either direction (even if they're not being displayed) to smooth the infinite scrolling, rather than having the user bump to the end of either side to load more (but keep that as fallback should the user scroll too fast). Give users the option to opt out of infinite scrolling to save bandwidth (they gotta use the bubbles pseudo pages then). Remove the OP post being displayed unless the user is on the first "page", with infinite scrolling theres no feasible way to view the OP to begin with (aside from being at the beginning of the thread.
Get the functionality down first THEN polish the thing. As is, its way too early to promote it on all pages of the old design. This id call an alpha relase at best. Definitively not useable for the broad userbase right now.
On the bright side, the loading image is nice. Yes, i dont like the new design.