Noisy? Yes, ECS getting better, but still too loud.
VNAV? Works fine for me, but I never use VNAV below 10K.
FMC? Getting better...
CPDLC? Works fine with new FMC updates
Radar? Mostly fine, certainly better than most manual efforts. Just have to understand how it works.
Galley? The sh!ts. Heard we have no one to blame but our own Mark 8 for that.
Grunt? For sure. GENXs are really nice.
Fuel? Same burn carrying 25% more than -400ERF. Seems pretty good to me.
Flight controls? Make hand flying a lot more fun than the -400.
Brakes? Yes, work very well with or without reverse. GENX reversers are very reliable as well.