This came just too late for me to benefit from. I was doing a project in Munich last year and traveling back and forth when Air Berlin went bankrupt (I was on their second last flight) and Lufthansa flights became a combination of stupidly expensive and unavailable. Door to door the plane took about 3.5 hours, which is pretty good. Most of that is waiting, dealing with security, and public transport, etc. The flight itself is less than an hour typically.

So, I took the old ICE a couple of times which took over 6 hours and indeed never really gets anywhere near it's maximum speed. They had a particularly slow variant taking nearly 7 hours. The new one should be a bit under 4 hours. So, the new line is very competitive with air travel and I'd prefer it over taking a plane. It's a much more relaxed way of traveling. German trains are pretty comfortable.

They could improve things further by eliminating stations from the route and improving the track. https://www.openrailwaymap.org/ has a nice visualization of the speed limits on different routes. There are only a handful of segments where trains can go full speed in Germany. If you look at the Berlin-Munich track, it only goes full speed about half of the route. IMHO, Berlin-Munich could get to about 2.5 hours but it requires a lot of investment. Faster if they get proper high speed trains. Compare this to France, which has proper high speed tracks and trains ride at 300 km/hour there.