#4 shot at f5? Wow! Whole lot of DOF.
That would be because the focus fell on the bridge behind them, not on the couple ... the couple is OOF.
#1 Cute pose, but a little too flashy and I'd like to see a tighter crop.
#2 Very nice! A little flat, maybe mess around with your curves a little to add some depth.
#3 They look stiff ... it's just never good to pose people on their knees, unless there's a row of people in front of them.
#4 Couple isn't in focus. Angle isn't great - you were at the short end of the kit lens, yes? Stepping back, zooming in and getting a little lower would have made this shot oodles better.

