There was a conversation on IRC a day or so back on this sort of thing, I checked my old news source bookmarks and not a lot were doing. I will leave the sources dump for now but
https://gbatemp.net/threads/does-gbatemp-have-a-rival-forum.355250/page-2#post-4785064 might be relevant here.
I assume we are not counting various reddit groups in this. Some of the youtube types, both older and newer, also have fairly large forums and are essentially independent, though I am not inclined to pick apart what ones are what and where CDNs come into all this. Equally I will stick to the English speaking side of things here.
Anyway
https://www.se7ensins.com/forums/ has historically some broad similarities, though they seemed to have leaned somewhat into the online modding side of things in recent years, with here and is fairly big.
http://www.nextgenupdate.com/forums/ seems quite big, don't know that I have ever landed there before though during a search though. As far as I can tell they are independent, certainly have the hallmarks of such a thing.
https://forums.penny-arcade.com/ exists, not as popular as it was a few years back but nothing to be sniffed at either.
https://forums.guru3d.com/ I believe are independent, most certainly count as big and have a decent gaming section in it. If you are looking for some ideas for things then these guys might be the inspiration for some.
https://www.avforums.com/categories/video-gaming-forums.517/ I occasionally get linked to, hard to assess how big they are for games as they are also very very popular in the audio-visual world. That said their games stuff is good. Technically they are owned by an AV consulting company but from what I can see it is more of someone in that world started an enthusiast forum way back when and it stuck.
Pushing the boat out a bit further you also have
https://forums.overclockers.co.uk/ , they are the forums for a PC parts vendor but they do fairly well for sustaining themselves in their own right.
Most of the other console/console family leaning places are not doing as much any more.
http://www.dcemu.co.uk/vbulletin/forum.php are around and doing things,
http://forums.qj.net/ are not anywhere near as popular as they were during the PSP scene's earlier days-mid days but still around.
Since the implosion of neogaf I certainly don't find myself landing many places other than here when it comes to searches, and to head off the obvious I frequently use machines and connections that have not visited here before.
After this most are around 10K user count range or part of larger magazines, which in turn are seemingly all controlled by one of about 5 companies. Several of said magazines used to be independent but this last 5-6 years has seen quite a few acquisitions. To that end I would expect a bit of run of "big" journalists going independent again before too long if history is indeed circular, doubly so now we have all those monthly funding things.