They can keep a lot of things they have achieved with Halo 5. Removing armour abilities we had in Reach and 4 but giving the standard sprint and the boost was one of the right things.
And it really is a mixed bag of complaints Halo 5 gets at the moment. Some don't want any real change at all, they'd rather have Halo like it was eight years ago.
Some only criticize the weak spots, ignoring the strenghts.