Uncharted series is one of those few games from which you can just take the cutscenes, add some more cutscenes instead of the gameplay sections (shortly depicting them) and you have a trilogy (well, considering the forthcoming Uncharted 3) of fun adventure movies with great characters and acting.
Half-Life movie would be something despised by fans, I think. I mean, there are short fan-movies based on HL2, yeah. But the story of Half-Life is really not THAT good, it's how you experience it that makes it cool, so Half-Life would have to get a bit of re-imagining to transform it into a good full movie, and most fans would hate that. Or the movie creators can make it the crappy Doom-movie way, which... well... the idea behind the Doom movie wasn't really that bad... it's just... well... Doom movie is crap, yeah.
Assassin's Creed could be transformed well into movies - though I think the Animus and the future storyline should be dropped for that kind of thing. Animus is really something that works GREAT in a video-game (and, well, I consider it to be the greatest justification of all the video-game conventions, but it's something I don't really dig in a movie), and I always loved the past-storylines more than the future (uhm... I guess that's present from the in-game perspective) ones. On the other hand, if the future would be interesting (it's really not in AC and ACII, haven't really played Brotherhood yet) then Animus could be modified to just watch the genetic memory instead of controlling them (well, in the game Desmond actually controls Altair and Ezio, that's part of the bleeding effect's existance as I understand). AC movie should not necessarily depict Altair's or Ezio's journeys, but those two characters have got very good characterization and character development in the games. And... well, I like them. And the Third Crusade setting is a great setting way underused in both movies and games, in my opinion.