So many things have changed with this new push to the site, it's honestly a little difficult to figure out where to begin, but I'll do my best. First off, the site's layout has been touched up quite a bit. If you're reading this, you've seen the new catalog and are also taking in the new thread view with greatly-increased margins. The new catalog also is purely CSS grid-based (no JS necessary) and will scale much better on large/high-resolution displays.
The other big feature that will jump out at you if you've frequented Futatsu before is the lack of the reCAPTCHA logo anywhere. That's right, no more botnet - Futatsu now uses captchouli to generate CAPTCHAs, without needing to phone home to Google or use JS in any capacity; in other words, the site is completely usable without JS once more.
The third big feature is live thread updating; unlike the polling-based method a lot of other imageboards/4chan extensions use, Futatsu will update threads your viewing with new posts the instant they go up (without saturating your connection). This currently isn't supported on IE/Edge, but this is easily fixed - I'm just not sure how many imageboard users there are that use those browsers.
A couple other things that maybe don't deserve near-paragraphs:
HTTPS support - I know some people requested this.
Futatsu is now completely CDN-backed - this should help loading speeds a bit.
* Upload limit has been fixed; you should be able to upload files of up to (at this time of writing) 5.0MB now.