I've had a fair bit of NPM installation issues as well and I am a big NodeJS supporter. Often their service is down. If you installed npm a long time ago, it likely doesn't work reliably with the service as it is now and you need to do an "npm install npm" to fix it.
Generally, npm needs to get more professional and I think they are trying.
Not to mention that every language has it's own package manager and all of them have a different idea of how to implement one - total not invented here syndrome IMO