I had multiple Nexus 7s... I'll start with the bad.
The speaker is weak and might be one of the worst speakers found in a tablet.
The screen colors are a bit washed out, particularly green and yellow if memory serves me correctly. Though if you aren't comparing it side by side with another tablet you possibly may not notice this.
After playing a video the screen will look oversaturated. This has something to do with the Nvidia Tegra Prism thing. Not sure if it was ever corrected, but there is a tweak for rooted tablets to disable the power saving feature that causes this problem. Otherwise the effect usually goes away after a few seconds by itself.
Early batches of the Nexus 7 had loose glass on the left side. I assume by now ASUS isn't having this problem with manufacturing.
Now on to the good. If you are looking at this as a e-reader, this is probably the most perfect tablet for that.
The Nexus 7 has narrow bezels in portrait mode that makes this take the most comfortable by far to hold while reading books, comics, manga, and such.
The soft touch back feels really nice to hold and doesn't leave fingerprints.
Tegra 3 is still a pretty nice processor compared to other popular 7 inch tablets (like the Kindle and Nook tablet using OMAP 4s). Runs games pretty well.
Overall for the price it's a freaking awesome tablet and the issues I list are mostly minor (though the speaker quality was a real downer for me).