I entered LH by code sharing with Singapore Air in 2001 and was baffled about the contrast between the one LH flight and the three SinAir flights.
No space, No (edible) menu, scarce drinks, unfriendly personnel on ground an on board. The entertainment system was the oldest of my four planes.The seating in the 747 was 3-4-3 and I got a window seat. No chance to get out for 10 hours. Or should I start an argument with to sleep simulating neighbors? No help by the uninterested flight attendants. No wonder.
What I know now is to check the small print on the offer not to get there again by codesharing.