I'm from Germany and currently commuting by ICE.
As a short explanation: DB consists of many parts as e.g.:
DB Netz - Provider of infrastructure
DB StuS - Provider of Stations
DB Regio - Provider of "Nahverkehr" (near-distance-transport, which is just ordered by the authorities of the 16 states)
DB Fernverkehr - Provider of long-distance-trains (ICE, IC, etc)
In nearly everything which happens in rail transport in Germany DB is involved this way. When your train is delayed, maybe it's an infrastructural damage or a failure on the train or on another train, DB is a part of the problem anyway.
So it is no surprise that DB has no good reputation although things are going more or less well. Punctualitiy in Nahverkehr is pretty good, in long-distance-traffic a little worse but more than 70% of all ICE/IC/... trains are just 5 minutes or less delayed.
Most problems people in Germany see with rail traffic are caused by politics. The federal government don't want to pay for infrastructure and long-distance-rail and the states already pay for all their own trains (RE, RB, S-Bahn).
Long story short: yes if you travel by train in Germany frequently you see many things that are bothering you, the delays, big gaps in timetables (yesterday evening I had to wait for nearly 30 minutes because there was no other train linking two >200.000-cities on a 7.5-km-distance, where up to 7 trains per hour are riding), inadequate information politics and so on. But from trips to seven other countries I know for a fact that we are not alone with those problems.
Best regards from ICE 121
PS: ICE is very nice, if everything works. But Wifi, sockets, AC, toilets, dining car, I guess there isn't one day, where everything is working as it should...
(I sent it by my phone, sorry for any mistakes)