When it comes to entertainment, I’m of the opinion that habits - - both those of the producers and the consumers - - never actually go away; they simply change form. So, like I said way, way back in my very first Comic Vine editorial, I don't think it's a coincidence that the Best Buy shelf is resembling the spinner rack more and more. What manifested in the smaller arena of the comics business will eventually manifest in this bigger multi-media arena, guided by the same "invisible hand" of demand. So, while we may look at all of this as an extension of comics right now, kids who are growing up on the stuff now are going to perceive it as something sui generis. They'll fall into the same habits we have without even being aware of the antecedents.  

In simpler terms, spin-off comic movies popping up shouldn't be a surprise, because spin-offs happen so often in comics that readers rarely even notice them anymore. == TEASER ==

What exactly defines a spin-off is tricky, anyway. Was the WOLVERINE movie a spin-off of X-MEN or, for all intents and purposes, X4 in the same way that the next Jack- Sparrow-centric PIRATES OF THE CARIBBEAN is basically just the fourth entry in its series? Would a DEADPOOL movie be a spin-off of a spin-off? Going back farther, would you consider any Wolverine title a HULK spin-off simply because of how he debuted in the 70s? Is the Punisher a spin-off since he started off as one of Spidey's villains? What it comes down to, I feel, is whether the character’s got enough conceptual weight to stand on his own. You might think that, say, Pyro is awesome as a supporting character in X2, but would you want to see an entire movie about him? When there was talk about a WEREWOLF BY NIGHT or movie, I wasn't sure how it could work, as that monster's basically just the wolfman in the Marvel universe. Take him out of that, and... he’s just the wolfman. 

Tom Pinchuk’s the writer of  HYBRID BASTARDS! &  UNIMAGINABLE . Order them on Amazon   here  &   here .  Follow him on Twitter:  @tompinchuk

If we think about it, you could say that the 2012 Avengers movie is just a spin-off from Thor, Iron Man, Incredible Hulk and Captain America. 
Elektra was a Spin-Off from the Daredevil movie.  
 
Spin Offs work, they just have to be made from the correct character. I think a spin off for Black Widow could work because she is her own character in the movie with her own unexplained origins and past mysteries. 
War Machine would be hard to pull off since his Super Hero origins were in IM2, and it's hard to see him away from a cast of characters already established as a joint group (ie. Tony, Pepper and Rhodes)

I think an important factor that decides a spin-off's success is whether it's truly stand-alone or building off of what was already established.
 
For example:
@sora_thekey said:

"War Machine would be hard to pull off since his Super Hero origins were in IM2, and it's hard to see him away from a cast of characters already established as a joint group (ie. Tony, Pepper and Rhodes) "

Elektra was a Spin-Off from the Daredevil movie.   Spin Offs work

A Venom Or Deadpool movie would be nice

I must admit Electra was a great piece of cinema.....................ok it was painful

" For some cases, yes a spinoff could work. It just depends on the character. For war machine,i dont think so, hes too similar to ironman. I mean not for a comic nerd but lets face it these Marvel movies have a larger audience then just us. I don't know it would be that successful, and may be confusing to others thats don't have a comic "background". The Ironman franchise too well known and has such a large audience, thats what people would be expecting. "

I think the spin-off could work, if done right but Marvel has proved me wrong 3 or 4 times now.

" If we think about it, you could say that the 2012 Avengers movie is just a spin-off from Thor, Iron Man, Incredible Hulk and Captain America..."

I think some spin off movies can work, it just depends on the character.  To me War Machine wouldn't work as a spin off, he is just another Iron Man.  He is too similar to the other character whose movie he came from.  I know James Rodes (spelling?) is a different guy than Stark is, but he wears a suit of armor just like Stark's Iron Man only painted different and with some more weapons.  His differences, to me, aren't enough to warrant a spin off.  
 

My guess is that a spin-off requires either a very skilled production team or a very recognizable character to work, possibly both.
A Wolverine spin-off from the X-Men movies was a natural prosecution since Logan is one of the most recognizable icons of the Marvel Universe today. This gave the product an immediate possibility to be recognized and appreciate by the great public (aka thos who don't read comic books on a regular basis).
On the other hand a decent probuction team, especially one that knows the character, is needed just to make things right. Elektra might have been a recognizable character, but the overall work of the production, starting with the awful script, killed the project even before the release.
 
Now as much as I love War Machine - he's probably my favourite Marvel character - I don't think that a spin-off based on him could work, because Jim isn't that recognizable for anyone outside the comic book community. While the casual reader might know him from a couple of issues, or remember him from Iron Man 2, the details will probably be too fuzzy to allow a quick definition of the character.
More than that, Marvel just made a major mistake in the past, the horrible script/execution of Elektra and Wolverine killed a lot of the casual fans' interest for spin-off movies, making them too risky.

As usual as spinoffs are in comics, they don't tend to work well on screen.
Most of the times they end up quite cheap or silly...I mean movie spinoffs..

" @Gylan Thomas: i disagree  war machine is far diff , he's a soldier  tonys a biz man  not a soldier, look at war machines firepower  and his own movie would clips iron man if it has a team like ironman did!  has to have  great writer , directing, actors, effects, movie score  simple plot such as  war machine vs ultron would do...bring in hank pym...add doom...one more cameo  say...banner....man u know how much money that movie would make?!!   now picture other spin offs with such caliber "

Elektra....... That all I need to say.....

I love War-Machine but a spinoff movie for him will not work.  To the general movie goer he's just Iron Man with more guns and a different paint job. 

Spin-offs can work if the character is rich enough and engaging enough to demand a sequel. In a lot of ways, I never understand why they do these spinoffs. Where do they get the idea that the public is clamoring for a Deadpool, Electra or War Machine movie??? Are people tweeting it up, dressing up like them for Halloween/Cons or are they just trying to astro turf some hype for a character that was liked in a movie??? 

Maybe a War Machine movie could be an darker/R-rated version of Ironman? Think of an The Expendables type of scenario, where War Machine is sent to take down a dictatorship, assisting the soldiers in that war. Put in some Paul Verhoeven or Saving Private Ryan, level of gore. I would watch that movie. Maybe they can put in some *nuclear missiles about to be launched to the US* type of scenario too. 
 
Edit: How about another idea, where this time, the dictatorship above, managed to keep Tony hostage and demands *insert typical rogue nation demand*. So War Machine is sent by the DOD trescue Tony as he is considered a valuable asset to the military. With that, we can keep War Machine relevant at the same time, sticking with the Ironman roots.
 
Then again, I'm one of those bastards that watches Commando too many times. lol.

War Machine and Black Widow solo movies could work since they have their own comic book series.