Just struck me that I linked to several analyses and suggested they reached a "near-consensus" but never really explained what that consensus was.

You can - of course - read the pieces yourself... and there are a lot more where they came from. But the basic gist is this:

1. The LibDems shed most of their seats rightwards.

2. The distribution (as opposed to the actual size) of the UKIP vote damaged Labour more than the Tories.

3. There was a perception that the economy was recovering (and people are ansty about changing governments in those circumstances).

4. Most importantly, and perhaps largely responsible for all 3 previous points... Labour failed to offer a coherent alternative to the tories.

There's no way of knowing whether a more leftwing Labour would have done better; but so long as they were offering "austerity light" (to use one of Corbyn's favourite phrases) they could never hope to hit the tories where it hurts.