Ignoring the story and fighting with the army or monsters, I rather enjoyed Prototype 1 as a open world, platforming across the roofs of buildings or running and gliding by them. Much the same way most people only really enjoyed Spider-Man 2 movie game for the web swinging, nothing else.
A game for the combat could work out well, if it was just focused on that and so I could give them money if they show me more that indicates it's more refined.
Prototype 1 had the best feeling movement of any open world game I have ever played (With SR4 and Spiderman 2 close behind).
It was also a ton of fun to just go ham on the city and blow everything up.
Prototype 2 is surprisingly ok, although the movement doesn't feel as good as the first game IMO.
Edit: Oh gosh I'm being crushed by the giant post above me help