I enjoy his three volumes and reread them every so often, but they are more than half a century old. So how do current historians view his work? Has later research shown any of his facts to be inaccurate? Are any of his points of view or interpretations outside the current mainstream?
Eh. They're ok. They have their problems - too numerous to list here - but also their high points.
If you've already read them and want a more modern opinion (or haven't and just want a book on the crusades), check out:
Runciman was writing a polemic. His history is solid - the facts are all there - but he's writing as a Byzantinist who detested the religious zealotry on display by medieval Latin Christianity. Just look at the very last sentence of the 3rd volume.
Riley-Smith's book is fine but really dry. I prefer Tyerman's God's War or Madden's New Concise History of the Crusades for readability.