This guy correctly leaked the title Fallout 76 and it's supposed genre 4 hours ahead of the official announcement as seen in this post.

He has since went on to share more supposed information about other E3 conferences:

Bethesda will have more to announce at E3, no Starfield

Kingdom Hearts 3 releasing this year

Death Stranding gameplay will be shown at Sony's conference

Sunset Overdrive 2, new Gears of War, Halo and Forza Horizon at Microsoft's conference

That Nintendo E3 Showroom Instruction document is apparently legit, new Punch - Out, F - Zero, Star Fox and titles for Fire Emblem, Metroid Prime 4 and Yoshi, Fortnite and Fallout 3 Anniversary

Cyberpunk 2077 will have a gameplay trailer

Possible nudge at ES6 being announced next year 

The Last Of Us 2 gameplay

Some of the stuff listed here is basically a given but there's some interesting titles in there as well. He'll probably post more in the near future, as it stands right now he's pretty credible.

Update - Shinobi now implying that Starfield won't be at E3 too

That Nintendo-list is so fake

How can be that lucky to guess the name "Fallout 76"?

Must be fake, no Playstation All Stars 2

Any leaks on Shadow Die Twice?

When it comes to the Nintendo document I think he's only saying fallout 3 is legit, not necessarily the whole thing.

The Reddit question is "is this legit, concerning fallout" his response "it's legit but not Bethesda's big announcement."

So yeah I wouldn't say he's saying anything about everything else on it.

Totally fake

These comments would imply otherwise. 

Who do you think some random Reddit poster is that has inside info on every major company? 

Some of those are so obvious haha, like Death Stranding being shown on Sony’s stage. Uh duh.

I call BS on Sunset Overdrive 2. Insomniac owns the SO IP, so they would have to be the ones making it; however, they have made it clear that their entire team is working on Spider-Man and that this is the biggest team they’ve ever had. And the games will surely not stop after September’s Spider-Man, so Insomniac will be working on Spider-Man for years to come.