Depends on the parties involved. If it was the extreme right that came out this strong, I would be worried. But Lafontaine's Left becoming part of coalitions in the West (and de-radicalising itself in the process) would be a good thing.
I predict 20% for the Left in the next Saarland elections.

"If you know your enemies and know yourself, you will not be imperiled in a hundred battles." Sun Tzu