From what I have herad - on arrival to the USA - can be a pretty unpleasant experience for some.
I've never know anybody who has described the experience as "unpleasant". If you enter the US via IAH or SFO the experience is a breeze with friendly CBP staff. In all my travels through those airports I've never taken more than around 20 mins or so from plane to leaving baggage claim. LAX is a different story though with this often taking around 45 - 60 mins in part because of the time Air NZ services arrive, and the fact the airport is so busy (and simply inefficient).
If you've done things which will exclude yourself from entering the US (and we've seen plenty of such posts in recent years) then it can certainly be an unpleasant experience. For the 99.9% of people who aren't in this category I'd describe the process as being pretty good, and certainly better than many other countries. Even LAX is a superior experience to most UK airports or EU entry points.