Of course there are quality new builds, which will be standing in hundreds of years, but there is a range of quality and many are not great.
If you buy a one-off new build or a very expensive high-end one, it could be solidly built and of high quality.
If you go for a 'help to buy' type house on a large estate, which is targeting those who cannot afford to buy without help to buy, the quality may well not be great. As others have said, the fact the tradesmen who work on these big estates say they wouldn't touch the houses with a barge pole, tells you a lot.
So what are the issues? Some of it is about the funding methods and the knock-on impacts onto quality. So estates which expect to sell large percentages of their new builds through help to buy have something of a captive market - people who cannot buy older houses which don't have help to buy available with them - so they can offer houses with thin walls which cannot hold pictures, or lofts which cannot store stuff, or roads which are too narrow for everyone to park their 2 cars, whilst only providing 1 parking space per property.
New builds on a big estate can be very different from a very small development or a small builder new build. But of course, the majority of new builds are those from the big estates, which is why people think of them, when they think new build.
Pros - warm, low bills, probably less large maintenance bills (like a new roof or boiler)
Common cons - smaller rooms, small gardens, sometimes away from the town/village faciltiies, more likely to be purchased with help to buy. Help to buy might allow you to get the property but you'll probably pay more for it over the long term - less good mortgage rates, fees for remortgaging at the end of the help to buy phase, often prices have dropped in that period or not risen at the rate of older properties especially if on large estates where totally new is still available and commands the premium over the 4-5 year old houses.
In my mind, using help to buy is very much like using a credit scheme to buy a new car. It costs more in the lomg term. And it's often those who can least afford to pay more who use the scheme and lose out.
If you like modern, then why not buy a newish rather than totally new build house? Usually, for the price of a help to buy, a slightly older, but still very modern house could be had, without the downsides of help to buy. Many people who've done help to buy now wish they hadn't had the new house with the 2 ensuites but an older one without and avoided all the re-mortgaging and drop in value of a new-build issues they experienced.
Even without help to buy, look at modern but not totally new build if that's the style you like.
And remember the tradesmen know something....that's why they wouldn't buy the ones on the big estates.