The demo was great the only downside of it was that it was kinda too short but did make nice contrasts between the 3 campaigns although if people got thrown of by Leon's campaign I can say it was the beginning of it unlike the Chris' and Jake's, that is why there was so much walking around.
And yes you walk with the left stick and look around/aim with the right but there is the option to switch them. The Summer Jam demo had already even more options added.
Speaking of pausing the game, yes you cant, you can only bring up the pda which will make u crouch, im sure they will add the option to pause the game if u r playing solo soon enough.
By Summer Jam Capcom confirmed that they r already looking into fixing the screen tearing issue, as for continues there are none cuz it was taken straight from E3 where it was up for promotion and showcase, if you die you werent allowed to play on, same reason there r no checkpoints.
Regarding the hud not showing up, i think there was an option bug ingame that made it disappear completely, it shows up every time u aim ur weapon and disappears after a while.
Besides the minor bugs, which they even warned about that there are, the demo was great. Id personally rather have the one they showed at Summer Jam though xD