Pros
T-Systems is actually a melting pot of small and mid-sized IT companies aquisitioned by Deutsche Telekom. Only two years have passed from the start at the time of this writing and up to now the teams coming from the smaller companies have kept most of their heritage, meaning your experience will vary depending on where your team actually came from in the pre-T-Systems era.
I believe my team is one of the more fortunate ones. We are one solid block with no internal tension but a lot of cumulated knowledge. I work for the company in a "partnetship scheme" which means the money is good but there are no benefits as you are not a company employee.
Cons
There is plenty of bureaucracy to slow you down.
