Here are my impressions after a day with the Switch:
I got the grey version yesterday with Zelda, the official case and Fast RMX. This is the first console I have bought at launch (well, before launch), the closest before now being the Wii U about four months after launch. What do I think so far? Well, it depends on what we are talking about. But to get it out of the way now, my overall feelings are positive.
First of all, the system itself. It's very nice. It actually feels like it's worth the (steep) price tag you're paying for it. There's just the right amount of heft to it, it's not too heavy but it's not too light. The screen is surprisingly nice. The 720p isn't at all problematic, the colours are great and it's pretty clear. Oh, and it's small. It looked small in the comparison photos but you have to hold it in your hands to truly believe it. I compared it to the Wii U gamepad and it really puts it to shame. The fact we are getting something so slick and well-made off the back of the Wii U impressed the hell out of me.
As for how it feels while playing, it is super comfortable. No hand cramps after 20 minutes like on the 3DS, and no clunkiness from the gamepad. Even the joy con grip (which I expected to hate but feels pretty natural) feels nice. I will still buy a pro controller soonish but the joy cons feel good in both docked (grip and separated) and handheld mode. And speaking of handheld mode, it can definitely be used as a portable system. I went out for coffee this morning and took the Switch with me. I used it in handheld mode in the car, and it actually felt like a handheld. Used it in tabletop mode in the cafe (with the joy cons separated) and that also worked really well. I also showed it to my friend (who plays on PC and PS4) and I think I made him want one a little! But overall, it can definitely be used as a handheld (though I wouldn't advise keeping it in your clothes pockets, but I've personally never done that).
The UI is a mixed bag for me. I like the design of it and how fast it is, but it feels somewhat incomplete right now. I know more functionality will be added, so it's not a huge problem for me at the end of the day, but (and I will echo this sentiment again at the end of this post), it makes the system feel rushed out. Another issue which makes me feel this way is the launch lineup. Aside from Zelda, Fast RMX and Shovel Knight (which I haven't bought yet), nothing really interests me. Zelda is absolutely fantastic and I think Fast is pretty good from the little I've played of it (and Shovel Knight is Shovel Knight I suppose), but at the risk of sounding melodramatic, it's kind of heart-wrenching that such a nice piece of hardware wasnt launched with a suitably nice lineup of games. Lego City Undercover and Mario Kart 8 are next month so I feel that this issue will likely fade away one they hit (especially the later which I looooved on Wii U). But Zelda is definitely the real deal. I'm generally not a fan of open world fantasy RPG's, nor am I a Zelda fan, but this game is the best thing they could have launched with.
Overall, I really like the Switch. Despite its shortcomings in terms of software, it's a very well designed system with a ton of potential. A powerful handheld that can play home console games and act as an actual home console seems like a great direction for Nintendo to go in. While the Wii, 3DS and Wii U's party tricks were all gimmicks, the Switch's party trick is versatility. Being able to take this anywhere, and play in a variety of different configurations is an attractive prospect. As I said before, potential. However, I just hope that Nintendo uses that potential to fix some of the current issues.
TL;DR: Great piece of hardware, kind of lacking on the software side right now outside of Zelda.
Edit: Haven't had the joy con desync issue either, but I sit at my desk with the docked Switch pretty much in front of me.