Yeah, they all still look pretty nice. The Japan missions look pretty rough in SA, though, and it doesn't help that those are the worst stages in the game. IO Interactive has never been great with animations or character modeling, but what I always felt was their strong-suit was crafting intricate sandbox levels with memorable atmosphere. In that regard, these three games look great in HD.
That being said, the art-style of all three Hitman games in the collection doesn't lend itself as well to the HD update as some other PS2-era franchises. Ico/SotC, God of War, MGS, Jak & Daxter, Ratchet & Clank... etc. all benefited more from their HD updates.
As usual with these HD collections, however, there is always something changed or removed that keeps these versions from being the definitive ones. In this case, it's the removal of cheats from Silent Assassin and Contracts. What a damn shame.