Center Channels are a big problem.
However, a lot of listening is done in two channel so the mains must cut it.
The center is probably the most difficult speaker of all to engineer. It has to be reasonably compact and yet handle high power. It must be very accurate with low coloration and be a point source.
Accurate conversational speech really helps the realism of movies.
However for Opera the center channel really has to do very heavy lifting.
The vast majority of opera enthusiasts listen in two channel mode, because the vast majority of even very expensive systems, have center speakers unequal to the task. A 5.1 or 7.1 BD opera production is absolutely the most demanding material for a center channel, by a big margin.
The Thiel SCS4 is the only commercial center I have heard that is anyway acceptable.
Of all the speakers I have designed, I think I'm most pleased with the performance of my center channel.
It is a highly damped TL with an F3 of 44 Hz second order roll off. The BCS is active and very precise for natural reproduction. It blends seamlessly with the mains and never draws attention to itself.
With the sources around these days, BD movies and other productions on SACD, it seems all speakers have to be highly capable.
For most CDs they are improved with algorithms such as PLIIx Music. It gives a much more realistic sense of space and correct ambiance and increases the depth and height of the sound stage. It does not work for all discs, but for most it does, especially if a minimal microphone technique was used.
So ideally all speakers should be highly capable. Unfortunately in most homes this is seldom practical.