I have ridden DB perhaps fifty times. There has been a consistently high level of service. The one time my ICE was delayed (because a maintenance window had to be extended) I was given a voucher for half the ticket value.

Buying tickets ahead of time on a particular departure can be a real cost saver and can make first class cheaper than buying the cheapest ticket at the station. Sometimes buying a ticket on Lufthansa to Cologne from the US can be cheaper than a ticket to Frankfurt airport. In effect they add the connecting rail ticket for negative bucks. You get frequent flier miles on the train too.

Before all the homeland security stuff you used to be able to check your bags to Cologne station and pick them up from a small baggage carrousel there. Now you have to pick up the bags at an auxiliary Lufthansa office next to the train station at the airport. Still, it beats having to schlep them all across the airport.