They're like short travel Model M keys with a lighter buckling spring sound.
The OKI is strange. On one hand it is a light switch with a buckling spring feel and nice click which is not so loud. On the other it is very cheaply built and is not so smooth when not hit in the center. Interesting for a collector. Mine was pretty expensive on ebay, and the few times I saw one after that, it was pretty expensive as well ($100 - $200 region). If you see one relatively cheap, you might just want to grab it to sell it to a crazy Japanese or Dutch collector. Those guys are gullible.
There is something odd about this keyboard, I've been trying to "put my finger on it" but don't really have the experience or vocabulary to explain it.
The core issue is, I think, is as you've described. That off angle key-presses react slightly differently. It's not major on this keyboard (it's effectively brand new) but it's enough to make certain key-presses sound and feel very slightly different, making touch-typing feel a little odd.
Obviously this keyboard hasn't been run in yet, there may be a bit of stiffness, the space bar does feel overly stiff. But if you're in a touch-typing position, the outer keys when pressed with your little fingers aren't hit straight on. As a result I think what's happening is that the qaz & [;. areas effectively provide a slightly different force curve.