One of the most scathing critiques of NEO is that it's incredibly centralized. There are only 7 validation nodes which are controlled by either Onchain (company that founded and is developing NEO), the NEO Council, or the City of Zion, three organizations that are very closely tied to each other.
More validation nodes can be added in future, let's not forget that NEO is still very young, it is yet to experience the explosion in growth that ETH had, and as such the validation network is still low. There is nothing in the core protocol that prevents new nodes from being added. NEO definitely has great potential, but it has a few growing problems, just like all cryptos have to overcome.