Entanglement. A lot of smart physicists have made a big deal out of this, but it is really not mysterious unless combined with some other effect. I recently posted about this.
Double-slit experiment. We get a similar interference pattern for any wave phenomenon. We would expect it for light, even with no QM.
Uncertainty principle. Not too surprising, once you assume a wave nature of matter.
Superposition. Like the half-dead half-alive cat. Just a useful fiction.
Many worlds. This is just a fantasy. You can have the same fantasy about classical theories, if you wish.
Identical particles. It is strange that all electrons are the same. It makes the world very simple, compared to the alternatives.
Discrete energy levels. This is truly one of the nice features of QM, but not usually described as mysterious.
Probabilities. Scott Aaronson says the essence is negative probabilities. I say there is no such thing. QM has regular probabilities, and so does every other theory.
Nonlocality. QM has no true nonlocality, in the sense doing something in one place causing action at a distance elsewhere.
Canceling infinities. These are mostly artifacts of extreme assumptions, such as having mass and charge concentrated at a point, having infinite density.
Linearity. Some other theories are linear, such as Maxwells equations.
Super-Turing computation. This would be interesting, if proved. Some say it has been. I don't believe it.
Lack of local hidden variables. Bell made a big deal out of this, but nobody expected local hidden variable anyway.
No counterfactual definiteness. This is closely related to the lack of hidden variables.