The result suggests a strong desire to give the other lot a go after some years of one lot - simple as that.
In fact, as was mentioned on this morning's Today programme, major switches from one party to another are not very frequent in British politics. Each major party tends to be the Governmental one for a few terms, then the other, and so on. For the many decades it has been mainly a Labour / Conservative match but the Liberals (pre Liberal-Democrat) have been in power, and their successor party does sometimes make significant gains.
That low participation, only 60%, is fundamentally much more serious. It suggests a widespread uninterest in, or disillusionment with, politicians and politics generally; not any particular party, individuals, acts or policies. That is something for all parties to think about, and I suggest starting with honesty in interviews, and wasting less time attacking their opponents and more time explaining their own plans.
I do not propose compulsory voting as some nations use. There may be a case for an "Abstain" box on the ballot form (the correct term in any election, not that childish "None of the above") - but such a poor turn-out is bad for democracy.
Similarly I do not want any sort of "proportional voting" - the excuse of those who support parties that prove of only minor popularity because they offer little enough to be attractive. Its likely effect would simply be a more diffuse version of the same result, making governing the country even harder.
I have no time for that daft "tactical voting" notion, which is insincere, even dishonest.
There is nothing wrong with our electoral system, which is "proportional" arithmetically anyway, but the lower the participation the weaker it is and the less meaningful the result. That applies to any voting system - no matter how pretentiously complicated, it still needs voters.
What is wrong is low participation!
Those too lazy to vote are the only ones who can truthfully claim their votes were "wasted" - but they can not and should not complain about the country's politics if they are too idle to participate.