That looks like a good sauce. Not knowing what you feel is missing or what flavor element you want to add, all we can do is guess.
To tune your sauce first be sure you have the salt-sweet-sour-bitter balance you want, starting with. If you want a bit sweeter you might add a bit of honey or molasses. If you want a bit more sour maybe some lemon juice. If you want to punch both of those. maybe sweet and sour, by adding both some honey or molasses and some lemon juice. How about the bitter side ? Cider vinegar has a bitter note that can be detracting. To get by that try substituting some plain rice vinegar or lemon juice.
After that do you have as much of the added flavoring you want - garlic, onion, etc. It may be just a tad more or less of one of those. Sometimes it's not so much a matter of adding something but rather taking something out that is complicating or confusing the flavor profile you really want.
Other flavor elements you might consider:
Paprika
Ancho chile powder
Ground corriander
Ground cloves
Ground allspice
For more and different heat
Chipotle chile powder
Ground Jalapeno powder
