Having spent sometime (throughout this day) using a Surface Pro 3, I have some insights and opinions from a normal (excited) consumer standpoint.
My thoughts...
Design:
From a design perspective, this device is pretty fantastic. Owning such computers as a newer MacBook Air, I can say that the level of quality is more than on-par with Apple's favorite offering. The weight feels very good in hand. When properly compared to a laptop (I say properly because it seems that the tablet-design has made many journalist compare it repeatedly to a iPad Air or Android tablet, quickly deeming it too heavy) it is extremely light. Compared to my Surface Pro 1 and 2 (which weigh the same) its is a substantial difference. Enough to make me look at my older Surface's in disappointment. Its very close to the weight on the Surface 2, so using it in "tablet mode" is a more viable option on the SP3 then it ever was on the SP1/2. Couple that with a bigger screen and its an overall winner. From my use, the aspect ratio was a wise choice on MS part. Using the tablet in portrait mode (yes, it can be done) does not feel awkward, look silly, or eventually strain your wrist. Could you hold the tablet at arms length (why?) for repeated use? Probably not, because its still has weight when compared to devices that would fair much better in, "arm-out" scenarios. The feel is great as well, if you've used a Surface 2 then you will immediately enjoy holding this device , as well. I personally enjoy the silver color as well, I think it brings more "life" to the device, as opposed to te dark magnesium.
"Lapability":
I guess I have to mention this area of the SP3. I find it amusing how this term is either hated or loved. I also find it funny that everyone is so focused on this area and how quick they are to dismiss its abilities. The above picture I was using the SP3 on my lap. Typing out this quick preview its been on my lap. When I first was using it I sat down (naturally) on a couch to use it. I can't understand the issues in regards to using this computer on your lap. I've tried various scenarios, seating positions, leg positions, it all worked. And not in a "Its-about-to-cap-side-and-hit-the-ground-but-if-I-hold-my-breath-everything-will-stay-still-and-wont-move" type of way. I just adjusted the stand to a good position and started using it. The kickstand is a GENIUS idea though and fully realized on this iteration of the Surface Pro. Multiple positions, great resistance (won't move if touching/tapping screen) and awesome build quality. The lowest setting plays VERY well for writing on the screen or using the onscreen keyboard with your palms resting on a table or your lap. Now, everyone is not the same, so my ease of use can very well be a disaster for the next man/woman. Personally, I feel MS has done a thorough job in addressing the qualms from the SP1/2 kickstand.
Performance:
Compared to my older Surface Pro 1/2 this thing is MUCH faster. It could be my own mind playing tricks, but I'm seeing usage out of applications like Po Tools on a much higher scale, than previously. One of my main reasons in wanting a SP3 it the ability to create music, completely, on the go through my normal software. Ideally, I'd like to have tried an i7 (the model I will plan to buy), but from my use with a i5/256 SSD/8 GB Ram, it has left me very impressed. Heat seems to be a none issue, through continuous use of the web from website , streaming, music, the device never became to hot. Warm? Yes, but nothing you would have to worry about. Battery length seems very good through my day, seeing real use and using it with a variety of different people. I have no benchmark test, but I'm notching battery life right where (if not better) MS has claimed. All in all, it has the performance to match a majority of users needs. Given the speed of the i5, my wife would be quite happy with the i3 because she doesn't want much more.
Pen:
There is a heated debate about MS choice to use N-trig over Wacom. I'll start first by saying, I am no professional artist, sketchers, painter, etch etc. My skills stop at stick figures and little brown houses on green hills, with the sun in the corner. I'm no authority on the nuances of pressure sensitivity and accurate usage. With that said, from my use with OneNote this pen feels WORLDS better then the original Surface Pro pen. Its smoother, latency free and much more accurate. It allows me to write in much more stable way. I take notes for a variety of reasons and personally use the Surface Pro 1/2 pen whenever I have either device. The feel of this pen is much more natural. I do have a artist friend who does work for marketing companies, graphic design using a Cintiq and had him try out the pen. From his perspective, it was just as good, he did mention feeling like it was "closer" to the screen when pressing it down to write. I mentioned the lack of pressure levels and his response was that it felt the same if not better. Take it for what it is or with a grain of salt. That's out of my "jurisdiction"" so from my humble OneNote application, it feels superb.
Price:
Given what MS achieved to create these devices, I do not feel that the pricing is off. Its right in line. The quality, build, feel, performance is priced very well, You want one of the best pieces of hardware/software, it comes at a price. That's my opinion, others may want it for $Free.99, but that isn't realistic.
Overall, I'm quite excited for the future of the Surface lineup. The SP3 is the step in the right direction for MS and one that I feel will pay off in the end. If your on the fence about whether this is the device for you, I'd advising giving it a test run in your local retailer first. Either way, I'd be surprised if you were not impressed.