The "genetics" in epigenetics can actually be quite controversial. That is, how epigenetic markers are inherited isn't very clear. In terms of DNA methylation, there are methylation maintenance enzymes. But for histone modification, how they are inherited (are they being inherited?) isn't very clear. Would enzymes that perform a certain histone modification being passed from mother to daughter cell during division be considered inheritance of the marker? The "information" for the epigenetic marker isn't being passed down, just the machinery is.
Anyways, there are still a lot of things to consider.
As a mechanism though, epigenetics is quite real. My old lab in some soon to be published results found a causal link between some chemicals secreted by an organism and epigenetic traits.
Sure. DNA/histone modifications do seem to serve some kind of purpose in gene regulation.
I just find it a bit amusing that people seem to hold these two specific mechanisms in such high esteem to invent a whole new term, "epigenetics" for them; especially when the inheritance of these mechanisms isn't well established. It's akin to the latest technological buzzword in the tech industry.
I am just being nitpicky here, but semantically, the term epigenetics applies to any mechanism that's not inherently related to the information contained in DNA. Transcription factor binding to DNA is technically "epigenetic". Any non-primary structures formed by DNA that produces some kind of function is technically "epigenetic".
The conventional meaning of the term now in biology seems to only refer to DNA modifications/histone modifications. It's just not a very precise term.
Anyways, there are still a lot of things to consider.