I've been to Birmingham recently and the station is much nicer than it was. It couldn't really be any worse of course!
The artists drawings I've seen on the Network Rail site look good, introducing natural light down into the platforms which is good, with a huge new atrium. Some good artist pics here:
http://www.networkrail.co.uk/aspx/6222.aspx
It must have been the worst example of BR 60s station designs. The old 60s Manchester Piccadilly was awful, but nowhere near as bad as NS.
I either read somewhere or someone was talking to me on the train about this while I was travelling there, that when they were building the new Bull Ring shopping centre the developers offered Network Rail the chance to build new tunnels underneath to ease the bottleneck. NR apparently refused (costs?), and the developers subsequently drove huge piles into the ground where the tunnels would have ran so it is now impossible to construct tunnels through that part of the city centre. I don't know how true this is though.
I quite like Euston, and the main hall is a nice structure, but agree about removing all the stupid adverts, put seating in, and announce trains earlier to avoid the mad stampede. The platforms need sprucing up though as they are dark and dingy.
I remember once waiting one rush hour for the Manchester train. The concourse was rammed, with loads and loads of people with those incredibly annoying pull-along trolleys, and they announced our train at platform 12 (or whatever it was). Stupidly they also announced in the next breath the train to Liverpool on the adjacent platform. So a good few hundred people surged down one of the side tunnels off the concourse that lead to the ramps to the platforms, and because of all the stupid trolleys everyone got tangled up and there was a complete logjam. It was quite funny as people were getting rather irate with each other.
Luckily I had my walking boots on so used them for what they are designed for and just climbed over the stuck trolleys - I was damned if I was going to have to stand all the way home because of the idiots and their trolleys!