We popped in last Sunday, when it was opened.
(As an aside, this prompted a promise to ourselves that we go into the city at least once a month. It's incredibly invigorating, and acted to recharge our mojo a bit. Both MrsLH and I are born-bred city folk - long periods of suburban calm don't suit us 
)
On the basis that nothing could be worse than the old New St., it's actually quite a sight.
For me, the best thing is now it's open, all the spaces around it link up and make sense. We went to the Bullring, from there into the station. From there into New St. itself via Stephenson St. . From there to Victoria Square, town hall, museum art gallery, Colmore Row, Chamberlain Square, Paradise Forum ... plus the High St. Corporation St.
And when the work on Paradise Circus is finished, that'll join on, giving access to Broad St. and Centenary Square, with Symphony Hall and the new library and Rep theatre.
All perfectly level for power scooters
The only downside (although it may yet prove to be a charm factor) is that some beautiful spaces are slightly overshadowed - the cathedral can look a tiny bit toy-like because of the surrounding buildings. However, this means there are a few little gems hidden from view - a bit like Soho square in London.
Come to Birmingham - it's not that shit.