I think that Dive Machines should be about the drop, but that doesn't mean being as simple as Oblivion. And the reason they should be about their drop is simply that, when they aren't, they are weakened with nothing to set them apart from any other roller coaster.
I felt that Sheikra's first drop was too hidden. It doesn't have the impact of Oblivion or Griffon as a spectacle ride. It's splash down is nice, but it's got nothing on Griffon's. You may think this has nothing to do with the ride experience, but it most definitely has.
Despite Griffon's beauty, and impressively landscaped first half, it's second drop/immelman combo is a complete waste of time that detracts from the impact of the first. Sheikra is a better ride, with forces that Griffon doesn't have, but it doesn't flaunt itself and it's a real shame because it leaves me we no lasting memory of it's greatness.
This is what makes Oblivion such a success, it is possibly the world's most successfully branded ride. It does something very specific, very well, and everyone whether they road it or not will remember it for the right reasons.
There are exceptions to the rule, but generally I think a roller coasters "type" should be the hub of it's focus. Coasters which use multiple elements, usually belonging to various "types", use their different elements as platforms for something else- usually an overarching theme or concept.
I think really, that's an echo of UCs point from a slightly different perspective.
It's hard for me to compare Nemesis and Inferno to other inverts, because I've overridden them both so much. Any enthusiasm I get for either of them could well be nostalgia and fanboyism, and any criticism of them could just be boredom.