Control systems are often extremely misunderstood.
Control4, Crestron, and AMX are all higher-level integration friendly units. Control4 is a bit more streamlined for drag-and-drop programming and from what I understand, really needs to operate with more specific components.
AMX and Crestron are open systems. The programming can be done at a much higher level and tends to be dealer specific. It can be done as simply as a Harmony - press a button, see things happen. But, it can also integrate with industry standard security switches, light sensors, weather stations, etc. It can go online and get data from standard sites. It can tell sunrise/sunset from longitude/latitude information.
Devices controlled are up to you. They certainly all make some proprietary equipment which is tough to control by others, but Crestron (as my expertise) HDMI switchers, are sometimes used within AMX environments, and the AMX system can control all switching and pass serial and IR commands through to Crestron directly via IP control. It's just not completely straightforward.
More often though, you can buy a Extron Radio RA lighting system and control it. You can buy your televisions from almost anyone with discrete commands (Panasonic, Sony, Samsung, LG) and control it just fine. You can get a Oppo or a Sony Blu-ray player. The cable box comes from whomever. Then your garage door opener may take some work, but it may be controllable via relays. Door locks the same way.
Anything that offers OPEN protocols for control can typically be controlled. It's not a closed standard system except for certain proprietary items, which you may want to purchase if they would make sense. But, typically it leans away from DiY installation/programming for beginners. You would really want to commit to it.
The plus side? I have 10+ year old gear from Crestron which is awesome. Their HDMI switchers are top shelf and basically untouched by anyone else on the market. Crestron basically financed HD-Base-T. They had it first, they had exclusivity. ... and you pay for it.
My home isn't done, it likely never will be. I'm not thrilled with Insteon which I use for lighting control. I like their switches, but their support for integration just blows completely. Scenes are difficult to set, and swapping devices and controllers is completely undocumented.
I keep thinking about adding my Nest to the system, but, WHY? I don't adjust the temperature very often, and they have a top shelf phone-based user interface.
My garage door and locks likely will end up on it, just so I can hit a 'goodnight' button and ensure my home is fully locked down. Add that to the lights to make sure the house is shut down for the night.
The biggest issue I believe that is out there is that there are many products which really are extremely proprietary. They talk up z-wave or others, but often don't have open protocols which can be controlled by anything and you really are stuck using their app for that, which may not allow for any universal remote to operate it. Then you really only have the choice of one or two manufacturers which may not work for you. Crestron and AMX, can quite literally control dozens or more of different types of motorized locks. Almost all commercial type (magnetic) locks. It can interface with many security systems. The list just goes on and on.
People who don't know anything about real control systems get confused about what Crestron, Control4, AMX, and others really do and use the word proprietary, when in fact, they are the only ones which truly can leverage their capability against almost any product on the market which allows for external control. It's just a very programming intensive process. You don't just plug it in, click a few buttons, and have a home that magically works.
The systems that allow for that, are extremely proprietary, and must be. They also tend to completely ignore the A/V portion of your setup entirely.
