It really hasn't. I don't think any of us are expecting it to go back to the "old" top gear or even fifth gear style of drab reviews, but it hasn't been like this for 10 years at all. It's got massively more childish since these three took over, and whilst I had hoped it would improve as time went on, if anything it's going the other way.
The jokes are fine, and I could even cope with the wetting himself gag. But as others have said, the BMW, vs Tesla, Vs Volvo might as well have been a bunch of 20 year old £1000 saloons and you wouldn't have been able to tell the differnce. Keep the silly karoke, keep the wee wee jokes, and remove the stupid ripped pants climbing from car to car scense and give us a bit more about the cars! It could easily go back to a middle ground giving us just a bit more information about the cars thmeselves and keeping the gags without having to be as over the top childish as it is now.
The show got a bit too boring when it's all focused on the cars. If you want to know more about the cars then read the manufacturers marketing materials.
The whole point of top gear, even back to the day's of Clarkson/May/Hammond, is to add a bit of immaturity to make it entertaining. Let's face it, you're never going to do any of the three of them did with the "company cars" in the 24 hours. And if they did a normal review on each car, lots of people will say it's boring.
Edit: Yes they could have just used three very old/cheap saloons, but I'm fairly sure they've done plenty of stuff before with low priced/budget cars.