You know what? Everyone should at least give it a try; in my opinion, it's the greatest thing Valve has ever released to the public. Unlike the complexity of Source SDK for those who aren't completely fluent in the Source engine, and the informal simplicity of Gmod for those who want something a bit more advenced, SFM is the perfect balance between the two. You don't need to be an expert to create some fine-looking content. Sure, it takes getting used to, but once you're beyond that, it's smooth sailing. Trust me, if you've ever wanted to make a neat poster or a structured video, look no further. SFM answers to a lot of things, and you should at least give it a little attention.
P.S. SFM is not constricted to TF2 resources, which I would assume some people believe. Any asset ever used in some form of the Source engine can be implemented into SFM. Sure, it may take some tweaking to get some assets working, but this is a rarity, and when this issue arrives, it typically is not that difficult to solve (a quick Google search will fix ya up).
P.P.S. Don't get scammed by people who host SFM poster commisions. Anyone can make a professional quality poster if they at least try to understand SFM, which really doesn't take that long. These SFM commisions are bad business >:c