I have a long-held theory: that for comics to successfully adapt to the screen, they need to keep the key visual elements of the comic with them, especially when those elements have been developed and refined over decades. You can bee too slavish about this (cf: Ang Lee's Hulk), but on the whole, comics are a visual medium, and they're very, very good at doing images.
So, whenever a new comics adaptation approaches, I always start my judgement with a look at how well the imagery matches those from the comics. Iron Man impressed from the start, with both armour and a Tony Stark that looked like they'd leapt straight from the pages of the comic, and certainly didn't disappoint on screen.
Now, the first wave of material on the sequel is coming, including the first photos of the movie version of the Black Widow.
How well does she match up to the iconic image test? Here goes: Here's the original Black Widow from a 1970s era comic:
And here's Scarlett Johansson as the movie version:
And the verdict? Well, allowing for make-up differences over the last 30 years - very promising indeed. Some suspension of disbelief is required (how is that hair ever going to be practical for superheroing/spying?), but otherwise very true to the source. A good sign.