I've put some thought into it... and I've decided I heavily dislike this new layout for many reasons.
There are a good many movies and games out there that are absolutely positively NOT meant to be witnessed in widescreen, for reasons like image quality, zooming, visual errors, etc.
Pretty much nobody's ever going to see the 46x46 icons people make for their submissions now.
It's fairly likely the double-sized screens would increase lag. I've tested this theory on a movie or two and haven't actually found that to be the case, but somehow it doesn't seem possible for it not to lag a little more when in widescreen.
Everything on every page is stretched out, and with the 0-5 voting system unaligned with everything else and the trophies and Flash information in a new place... it looks horrendous. Complete garbage.
Any movie without a play button or a preloader will start automatically without giving a chance for the rest of the page to load. With pop-ups and the old dimming-lights setup, this was never an issue. There should be a way to be able to start a Flash and THEN have it start loading. Say, like a "" button!
Where did the age rating go? Out of curiosity, I've checked a couple of Adult-rated movies and games, which I now almost regret seeing, but it helped me to know to avoid them later. Now you can't even tell what kind of movie you're going to watch.
And those are just a few of many more mistakes I could easily find.
Some of the suggestions mentioned earlier in this thread I thought would be very nice.
1. Glaiel-Gamer mentioned the possibility of a no-widescreen-option when submitting. This is a feature I personally would immediately use for all the Flashes I've already submitted to Newgrounds.
2. Others have mentioned the possibility of an account option where you could switch back to the old layout and not have to worry about any of the new flaws.
3. My favorite suggestion of all (and the most common one) is that the whole layout be completely changed back.
To quote livelavalive, "this actually makes we want to stop making flash."