Have you downloaded the Nintendo Switch demo for Dragon Quest 11 S? You should! It's free! It's also visually comparable to the PlayStation 4 version of the game, as a recently uploaded side-by-side comparison video demonstrates.
The video, which you can find on the "ElAnalistaDeBits" YouTube Channel, shows how carefully Square Enix handled Dragon Quest 11's Switch port. There are definitely differences between the versions, but they're almost unnoticeable unless you examine them side-by-side. Even then you're looking at negligible changes: The PlayStation 4 version of the game has shaper textures, lusher backgrounds, and better environmental effects (you really notice the wind blowing through the leaves, and the transparency of the water), but the Switch's character and monster models are practically spot-on. More importantly, The Switch iteration of Dragon Quest 11 doesn't seem to drop frames. It runs at a near-constant 30 FPS.
The comparison video also compares the PlayStation 4 and Switch versions of Dragon Quest 11 against the Japan-exclusive Nintendo 3DS version. Obviously, nobody expects the 3DS's graphics to come anywhere close to the other versions' visuals, but the 3DS game carries its own charm. The character models are surprisingly expressive.
I'm playing the Dragon Quest 11 S demo myself, and I'm impressed with the quality of the port. If I hadn't seen the comparison videos, I wouldn't think much is missing from the Switch version. The demo is quite long—10 hours by some reports (though people who've played the PlayStation 4 game report getting it done in six hours or so)—and I haven't gotten much further than Cobblestone Tor, the opening area the video shows off. The demo's reception has been very good on social media, which indicates the port's quality probably holds up through the whole game and not just through the first little bit. If you decide to give the demo a try for yourself, your progress will carry over to the retail version of the game when it comes out on September 27. Quest for dragons without fear or hesitation, young fighter.
I can say this much already: The orchestrated music on the Switch sounds much, much better than the PlayStation 4's synthesized tracks. That might be worth the price of admission by itself, but it's only the start of the Definitive Edition's bonuses. There are extra quests, tons of tweaks, new story content, and the option to play the game in a 16-bit mode. All this, plus the always-handy option to play the game in handheld mode. If you missed out on Dragon Quest 11 when it came out last year, now's the time to stop draggin'.