TOS was nearly the only ongoing franchise that still had the original cast in its last outing. Everything else, from James Bond to Wild, Wild West to what have you had recast, many more than once. I hate to say it, but it was time.
My one complaint is actually the reverse of many here: the update of the look and feel of the ship, and its equipment and technology was almost too long in coming. Every other franchise had adapted to new real world technologies, and updated their look accordingly. The actual, original TOS tech in no way reflected what we knew about how technology works, and was dated. Fan series' reflect this dated look in every installment, and even as I enjoy the effort the fan series' go to to entertain, I wish the look had been updated to reflect a better understanding of how the technology would be used.
I know there are those who are quite vocal about saying and believing the original TOS tech is supposedly superior, as the idea that simpler control surfaces that do more seems to them to be more advanced, but that isn't the way technology works. For instance, the cockpit of the F4 Phantom is complex for when the aircraft was designed and originally built, but modern military aviators find it simple. The cockpit of the F28, on the other hand, even with several touchscreen controls and display screens, is much more advanced, and complex. This is because more controls need to be in the F28 cockpit to operate the many more things the F28 does. What I'd really like to see is a balance between touchscreens and physical controls all across the ship, but especially on the bridge. There are always those controls that that is the only thing they should do.