It is a reasonably big step up.
Compared with most singles the speed increases by getting on for 50%. If you have not flown a complex single, the complexity increases significantly, and if you have it is still a step up.
So, for an average PPL with low hours and training aircraft experience, you will need to get use to:
1. the scenery going past a lot quicker,
2. the need to think a great deal further head, both in respect of nav and in preparing for joining the circuit,
3. potentially some new elements of managing the aircraft to consider - non welded gear, vp props, synching the props, cowl flaps, greater consideration of general engine management, more complex fuel management, hopefully a decent autopilot,
4. almost certainly a lot heavier handling - sort of driving a bus compared with a car.
In short it all adds up to a significant amount going on at first and undoubtedly the feeling for a while that you are once again well behind the aircraft.
They say, as they would, that you only become a professional pilot once you have an MEP!
If you are flying for fun, have less than a few hundred hours, and arent going to fly 50 hours or more a year - I wouldnt bother, unless you are better than average you will always be behind the aircraft. Get some more time in singles first and you will get a lot more out of twin flying.