Sorry if my thoughts end up being all over the place. I think a big problem with people who critique movies these days is that:
1.) A lot of different people/groups are doing it.
2.) A lot of different people/groups are doing the same movies.
There's only so many times you can hear people make jokes about Tommy Wiseau's accent in The Room or the nipple suits in Batman and Robin, or how everything is blue in I Know Who Killed Me before you get sick of it and there's nothing left to say. Yes, Batman and Robin is very homoerotic and the piano teacher in I Know Who Killed Me is wearing a Liberace style ring. Please stop pointing it out.
I used to read reviews on agonybooth.com and retrocrush.com ages ago. I sporadically watched Nostalgia Critic videos a few years ago. Currently I listen to a podcast called How Did This Get Made and watch Red Letter Media's videos whenever I have some spare time. There's a lot of overlap in the things they discuss and sometimes people bring a new perspective, but sometimes I find myself thinking "yeah, I know this is a popular movie to shit on, but maybe let it go and do something else".
I think the key to being successful when critiqueing shitty movies is to be either hilarious or provide inside knowledge. Preferably both. Also, don't focus on something really specific like nostalgic and retro things. Retrocrush and X-entertainment were hilarious sites, and the owners obviously had really life things that kept them from updating their sites like they did during their glory days, but eventually you reach a point where there's nothing left to talk about and you either have to stop or rebrand yourself, and fanbases usually don't like it when you do the later.
Yup. I know the feeling. First off, a lot of people tend to get into the whole reviewing aspect (or webcomics) or whatever because they want the exposure and money people like AVGN or Nostalgia Critic get. But even if you're not that ambitious, if you want to rag on Shaq Fu or Star Wars Episode I, take a number. The second thing is making original content is hard to do. One of the cool things about X-E was he had all this material to work with--old VHS tapes, promotional cereal stored in the freezer, McDonald's ephemera...but you have to actually write and document that stuff, and it burns out a lot of people. That's why cool sites tend to go under after their updates slow, fans leave, the site remains up as a living museum to once was (a lot of blogs are like this).
Even if you are a success, there's still cycles, and I think that a lot of reviewers are past their expiration date on this. I'm going to use some Forumer avatars to make my point (only used an example)
Step One:

begins to make YouTube videos. At least one is a surprising hit with a substantial number of views. People seem to like what

have to say or find

funny.
Step Two: As

begins to gain more views, his camerawork gets better, videos get longer, the "universe" starts to expand, and a steady fanbase and subscriber count is formed. This is generally seen as a golden age. Imitators pop up.
Step Three: As new subscribers begin to slow, content at this point is still good, but

is starting an unfortunate trend of using overused jokes and new characters like



.
Step Four: The ego goes to

's head and they start "phoning it in". Content begins to deteriorate, and subscribers plateau. Fans may hate at least one of



because they're lame gimmicks (and gimmicks are increasingly seen). A string of bad videos or a scandal of some sort will cause a substantial downfall.
Step Five:

videos slow as subscribers hemorrhage. At this point, the


may still be active but never get a following. At this point,

may still be getting money but relevance and subscribers flatline.