I agree with everybody else.
Three gotchas going from C172 to PA28:-
(1) Numerous instructors will advocate extra speed on approach. You really don't need it - stick to the speed in the manual.
(2) The manual says not to use use carb heat on approach unless there is evidence of carb icing. This is rather different to a C172 where it's pretty much mandatory. I have 100+hrs on a -161 and never saw signs of carb icing with, or without, the carb heat including right in the middle of the icing curve.
(3) No door on the pilots side, which is irritating as you can't get your pax strapped in then have a last walk around the aeroplane.
Apart from that, they are pretty similar to fly, enjoy.
G