I never had an issues with build quality, but I have also read about the things you are referring to. I don't know much about the L1, though they are supposed to be quite good. The VModa M100 is supposed to be out soon (I think) and might be worth considering. It will likely has a slight bass tilt, but it may not be too overpowering. I had the M80 and enjoyed the sound, but am not a huge fan of on-ears. The build quality will undoubtedly be top notch as my M80 felt indestructable.
I've read on this site that a lot of people raved about the so called MrSpeakers Mad Dog. Is this a good headphone for my tastes? :)