Resistance: Fall of Man overall looked pretty good to me though, maybe not very colorfull, but IMO that wouldn't per se have helped the target atmospheric feeling for this game, at least not like it does for a game like Ratchet & Clank: Tools of Destruction. Most importantly I liked the story and gameplay, resulting into me eagerly wanting to experience what's going to happen in the next release!
With regard to Killzone 1, I read the game mainly suffered from technical limitations and issues, many reviewers stated this game aimed too high for the PS2. This and other criticism judging from the demonstration videos have been dealt with and the basic concept greatly imporved upon, Killzone 2 has become a much MUCH larger project than the first title was.