Just checking in to say that I got my Surface Pro 4 Core i5, 256 GB, 8 GB RAM yesterday from Microsoft Store pre-order. Compared to the SP2 I have, it is so sleek. I really like the contrast between the metal matte case and the highly reflective Windows logo (which is already getting finger prints all over it

). The screen looks amazing with its high resolution as well as vibrant but not oversaturated colours. The pen is much improved over the SP2's pen even though, on paper, they have the same pressure sensitivity: the cheap plasticy SP2 pen was probably holding it back. The textured nib on the new pen makes it feel so much more like you're drawing on a frictional surface rather than gliding over glass. The edges are still a problem where, in the outer 1.5 cm, the cursor starts lagging a ton behind where the pen actually is.
From what I've read from the Anandtech review, thermal issues have been resolved from the SP3 where CPU usage only brings it up to ~60 degrees Celcius (compared to 80+ degrees on SP3). In my own use, even running at 100% CPU, it's not that uncomfortable to handle. The fan, however, is about as loud as it's ever been.
One last thing I want to touch on is the incredible PCIe SSD that's in there. That thing is incredibly fast given that it's in a tablet. I can basically confirm Anandtech's CrystalMark bench that has the sequential read speed at 1500'ish MB/sec. My sequential write speed was a little slower than Anandtech's at 300'ish MB/s but my SP4 was already filled up to 45% so that might have affected the write speed. To put this into perspective, my SanDisk Extreme Pro 960 GB SATA SSD (admittedly kind of full at 75%), which is still one of the fastest consumer SATA SSDs, benched 275 MB/s for sequential read & write. Basically, this thing boots instantly and loads programs incredibly fast.
So, yeah, first impressions but I'm quite happy with what they've put out. I haven't tried any games on it yet since I'm still installing actual work-related stuff on it but I'll try some out later