I'd already seen an opera based on the story of Saul, Carl Nielsen's Saul og David(though the Handel is really an oratorio). I must say, I don't find the story itself particularly dramatically compelling. Saul loves David but then when the people accuse him of only having slaughtered thousand whereas David has slaughtered tens of thousand, he gets upset and jealous and then dies after a dead prophet channeled by a witch tells him how much he sucks. Whee. Okay okay, that's a bit reductive, and you certainly could make something of this, but it would definitely need some work.
This doesn't do that work, really, but apparently Handel was really obsessed with this one (apparently, he had a bunch of specialized instruments commissioned just for it), and it very much shows. Lots of great music, choruses especially. It transcends its subject matter, and it's totally great, even if the title character is pretty cartoonish. Well, in fairness, this Glyndebourne production doesn't exactly make him any less so. He's kind of goofy-looking, and sort of flounders around the stage a lot. I mean, Christopher Purves is fine, and acts the role well, but it is what it is. It's a somewhat surreal production, mainly in costume contemporary to Handel's time, but with notable weirdness. Iestyn Davies is very good (GO COUNTERTENORS!) as David, even if he doesn't have the stage presence he might. Then again, that might be the fault of the oratorio itself, which doesn't necessarily give him the prominence he needs.
You (by which I mean "I") sort of feel like an oratorio staged as an opera ought to be instinguishable as anything else, but that's really not true. There's always going to be a level of abstraction that you don't normally find in operas. A chorus that doesn't necessarily correspond to any possible actual characters, people not really talking to each other...I still prefer them to be done as such; gives you something to look at. But still. That said, this production does an excellent job of feeling as opera-esque as it possibly could. My Handel fanboyism has not abated.