Of course, these screencaps aren't even in HD (or Blu-ray, as the final release almost certainly will be); they are only compressed elements in a video on Vimeo. Still, you can clearly spot the difference between the transmission master and the restored film. (Both of these examples are from 'The Adventure of the Clapham Cook', the very first episode, shot in 1988).
Series 1-4 have already been released in the US and Canada by Acorn Media, and Series 5 is scheduled for release in late June. I recommend the reviews from Blu-ray.com: http://www.blu-ray.com/movies/Poirot-Series-1-Blu-ray/32957/#Review. This is also a good place for fantastic high-quality screencaps from the remastered episodes. Here's an example, in comparison with one of my own screencaps from the previous DVD releases:
For the rest of us, let's hope the wait for these astonishingly improved films won't be too long... (I would make a guess at a 2014 release for ITV's complete box set).