On the main page you can't collapse sections like Gaming, Microsoft Extras, Wearables, etc.
Formerly those could be collapsed if you no did not regularly go into those forums. Even without the sub-forums showing in the main page (another issue, IMHO...*) the scroll time from top to bottom on the main page is way longer than it needs to be.
If the point of removing the subs from view on the man page was to decrease clutter and scroll time, then why do away with collapsing sections? Collapsing sections decreases clutter and scroll time. So the end impact of removing subs from view on the main page is more than negated by removing the ability to collapse sections and increasing font sizes. If the point of removing sub-forums from view on the main page was for other reasons, those reasons are lost on me.
*Removing the sub-forums from view on the main page makes the forum less efficient. Take HP Phones for example, this is a non-post area needed as a Forum Header. Users can not post to it as it is just a place holder. Right now it only has one sub-forum, HP Elite X3. Formerly users could click into Elite X3 from the main page. Now they have to click into the null HP Phones forum first and then select Elite X3. There are countless more examples where getting to the information you want takes more clicks than it should.
*Removing the sub-forums from view on the main page makes the main page less informative. For example, look at the Windows Phones section, Microsoft / Nokia Phones forum. You can't tell what lies within from the main page, so you click in and see all the sub-forums. Again, the main forum is null as Microsoft / Nokia Phones is a non-posting area. There is no need for anyone to click into it if the subs are on view on the main page. However, If I click into it and scroll the list, I don't see Lumia 810. Maybe that is the Nokia phone I want help with. Why isn't it there? Maybe I assume the board doesn't have an 810 section. It looks like the started with later models in the x20 and up range. Certainly the main page won't reveal that Lumia 810 is in the Windows Central Archive section under the Nokia forum.
If the changes were cosmetic for aesthetic reasons, I guess it is well done.
If the changes were for functionality, the end results are not readily apparent to me. Navigation time is increased drastically for me and I would humbly submit that I know the forum layout very well indeed. If I were a new user who had no idea where things were placed I might assume this board had very little content and I would likely give up before finding what I wanted...