Bad ui responsiveness, inaccurate and janky touch controls, slow to launch programs. Miserable to use, felt more like a (relatively solid) competitor to netbook-class devices than serious laptops, or iPads.
Not sure about the SP3, but my SP4 (which, btw, had no problems running Linux) was afflicted by the so called "flickergate", and I didn't manage to replace it. Since then, I sworn off any Microsoft hardware. Their software and OS, I had sworn these off years before, which makes these devices even less appealing...
This time, I’ll believe it when I feel it.