Looking around at some reviews of the U2311H the peak luminance seems to be just under 250cd/m2. This is a lot lower than the 440cd/m2 we achieved on the XL2370. Having said that - 250cd/m2 is actually a very comfortable and still pretty bright level for watching movies. When you consider a nice deep black level and good variation in the colours that the U2311H provides at this brightness level then I'm sure the viewing experience is very good indeed.
Some people just prefer the in your faceness of extremely high luminances, but other people find themselves turning down the brightness anyway and don't mind. It really depends how bright you like things.