There is an HD iPad version of Monkey Island 2. Can I play that on my iPhone 4? I know the resolution of the iPhone is slightly lower than the iPad resolution, but probably still higher than the source material. Will it run at all? If not, when will we see iPhone 4 HD versions?
You can't play iPad (labeled HD or not) games on your iPhone 4 because they are specifically made for iPad and they reside in their own iPad App Store ecosystem. As for iPhone 4 "HD" games; we won't see those. Devs only update their iPhone games to support the Retina Display's higher resolution. Hope that helps.
I'm feebly hoping that once the iPad jumps up to OS4, there will be a new display option with iPhone games using retina resolution.
Compared to iPod Touch/iPhone to iPad, the transition to iPhone 4 is seamless and the gain in definition depends on the size of the source images, not the original size of the display. This seems very different from what Apple did with the iPad, where it would appear that the x2 definition just renders to a ~480x320 frame, then enlarges. I will be much surprised if an iPad/OS4 (or even an OS3.2 upgrade) combo cannot render images at iPhone4 definition in the future - however... displaying iPad games on retina display would likely come with a decrease in ease of use: I had to scale the UI down to adapt to iPad (and that's just the first step towards a great UI for iPad). Conversely, we'd have tiny, hardly usable controls for some titles if moved from iPad to iPhone 4.
Yeah, I would think this mainly a one way conversion as not only would this render iPad game controls microscopic, they'd be likely positioned very awkwardly (like all VERY close together on either side of the screen for what, on the iPad, would be easy thumb reach on either side of the screen).