I have a Dell XPS 15 and, while it is a good laptop, it is not on par with the MacBook Pro. I will tell you why:
1. Build quality. Everybody praised the build quality. Materials may even be good, but the build quality is not on par with a MacBook. You can feel that the laptop is not half as solid as a Mac.
2. Trackpad. It is better than most Windows trackpads, but there are some issues that prevent it from being as good as the MacBook Pro's trackpad. In the beginning, the trackpad lacked sensitivity in some gestures (especially subtle touches to scroll up or down); this issue appears to have been fixed by new drivers. You never know, though. Disappointed as I am with the trackpad, I use a mouse. One of the reasons why I bought a Windows laptop was because Bootcamp support for the trackpad was so poor, so I chose a laptop which supposedly had a great trackpad. All reviews were saying that the trackpad of the XPS 15 laptop was finally on par with the MacBook Pro. It may be if you review the laptop for a day or two; but you notice it isn't after using it for months.
3. Keyboard. The touch of the keyboard is not as good as the one in the MacBook Pro. Plus, there is an issue with the space bar; sometimes it registers two key strokes. I've read this is a common issue in the XPS 15.
4. Palm rests. The Dell XPS 15 seems to run hotter than the MacBook Pro. This may be just an impression. The real problem for me is that the carbon fiber palm rests on the XPS 15 get hotter than the aluminum ones of the MacBook Pro. Plus, they get dirty easily and are not very easy to clean.
5. Webcam. The position of the webcam is awkward. Everyone has already pointed out this issue, and it is obvious.
6. Screen. The screen resolution is great, 3840x2160 (but, honestly, it is not a huge difference from a 2880x1800 retina display; I barely notice it). But it is more reflective than the display on the MacBook Pro. Color accuracy is not so great. The screen is very colorful and colors look vivid and bright (sometimes a little too much to be accurate). Darker colors tend to look a little bit washed out.
I think these were the main issues. I got a Signature Edition, so it comes with no bloatware. I wouldn't mind having the bloatware, though: you can always remove the software, or format your laptop. Not really an issue here, but it is nice to have it without the bloatware out of the box.
In addition, it is a really powerful machine. Specwise, at the time I bought it, it was superior to the higher-end 15" MacBook Pro, even though it was cheaper than the lower-end model. But, as for build quality, it is not the ultra-high end model that Dell wants you to believe it is. And it may come with several issues with the keyboard and the trackpad.