In Bavaria, the Conservatives have historically dominated so its no shock the SPD came behind the CSU, however losing so badly to the Greens is not only a shock a humiliation.
Furthermore its a clear sign that if Socialist Parties take a "Blairite" path and resist a return to Left-Wing politics (like with Corbyn in the UK) then they face humiliation in elections.
In the previous elections in Bavaria (2013), the SPD got 20% of the vote. Back in 1998, they obtained 29%. During this time, the SPD has roughly taken what we call in the UK, a Blairite path.
Currently the national government of Germany is a coalition of Conservatives and the SPD with SPD having senior cabinet positions such as the Vice-Chancellor and Foreign Minister.
The decision to continue to be pat of the Government was heavily resisted by Left-factions within the SPD however as those factions are relatively weak (in comparison to e.g Momentum's influence in Labour), the SPD joined the Government.
SPD-Right have been critical of Jeremy Corbyn's and the Labour Party's shift since 2015 and always held the theory that European Socialist Parties can only do well in elections if they "take the centre ground."
Well this result and a number of other results across Germany show that their theory is wrong. For example in two weeks there are state elections in the German state of Hessen and the polls are predicting the SPD to obtain 8% less of the vote than they obtained in the previous election.
The SPD are losing support mostly to the Greens and to the AfD and while from a left-wing point of view, its wonderful to see the Greens doing so well, it is of course worrying to see the rise in the AfD.
The rise of the AfD is certainly causing worry in Germany however the positive is that this worry is being met with political action. Yesterday a huge demonstration in Berlin of over 100,000 took place and with the German youth in particular, the AfD will struggle to enter any coalition in a German state as it will be met with overwhelming resistance from the street.