One of the least reliable components seems to be some sort of "transmission" that changes the ships from one means of propulsion to another. The transmission seems to have the reliability of the 1930s/1940s H-O-R diesel engines in some USN submarines. Though so far the transmission hasn't failed during a combat area patrol.
Another innovation that didn't pan out was the concept of weapons modules that could be changed to fit particular missions, with modules being changed in a matter of hours. Reality was fewer modules than intended that took days rather than hours to change.
In general terms, it looks like too much experimental cool stuff got stuffed into a too small package. The things from stem to stern and keel to mast seem to be big cranky laboratory curiosities not ready for blue water service.