Well, Rajoy and the Partido Popular are the losers. That's about the clearest result. Ciudadanos lacks the historical-political baggage of the PP, and can be expected to take over as the dominant non-sociliast political party in Spain.
I don't think there's anything to indicate a full-scale replacement occurring
outside of Catalonia. There's been a lot of defection with C's now polling 15% or so, but the PP are still polling like 30% themselves.
The PP within Catalonia have been marginal for a long time, they were on like 15% of the vote even 15 years ago. Their fairly angry centralism alienates a lot of the non-secessionists, too. There's a large chunk of voters who favour the current (or greater) decentralisation, and have a Catalan identity, these are voters the PP just cannot reach.
It's because of the PP's incompatibility that the non-socialist constituency used to be heavily with the CiU, which until 2010 was a centrist/liberal, vaguely nationalist but explicitly non-secessionist party. However, it must be said that the non-socialist constituency
does overlap a fair bit with Catalan nationalism, and the CiU followed/led/moved with that core towards explicit secessionism.
These days the section of the non-socialist population which doesn't truck with nationalism and secession is presumably mostly with C's.
If I had to guess, C's may have also also picked up some of the
stridently anti-nationalist left because the PSOE's local counterpart is a bit softer on the question than the fairly rabid anti-nationalist Ciudadanos. Locals might be able to correct or confirm this for me?