Something that scares me regarding domain names is their variable cost. I purchased a .sexy domain for a joke website and its price got raised by +70% less than one year after that, making the joke a lot less appealing. There’s no guarantee that when you purchase a domain name it reasonably stays around that price for years. Build a business on a domain -> the name increase by XX% -> you’re screwed and must pay.
.sexy is about 60-100$ per year. If you've build a business on it, paying double the amount should not hurt.
For me the most important thing about this new gTLDs is more about reputation of the gTLD registry. What if these go out of service? I'm pretty sure that there exist a protocol for that case, but I'm also sure that domains in a less popular new gTLD space might get far less protection from ICANN than any non-sponsored gTLD.