Changes between the old and the new versions are minimal. The new logo may be considered a little simpler, which is the current trend in the companies. Personally I think that getting rid of the red ”text box” was a good choice, but also that changing the colour from red to black was a bad one. The latter causes OnePlus’ logo to lose its identity and look overly similiar to other brands.
It can be argued whether or not the change had a point. OnePlus is supposed to release a statement about why have they chose to do this. If so, we will let you know.