The game focuses on stud collection, but the multitude of various bugs make 100% completion near impossible.
First off, I found traversing the Hogwarts grounds slightly confusing due to some questionable layout design choice. The developers seem to be aware of this as they provide you with a ghostly guide to show you the way around during the story mode.
The developers seems to have steered the focus on this game towards collection rather than the iffy platforming and combat of the previous titles. This is great as everyone knows that the real fun in Lego games is bashing stuff and collecting stuff right? Well that's what I thought until having got to 97% completion only to find out that a glitch was preventing me from getting the last two character studs and another glitch was preventing me from earning at least two trophies.
Determined not to let this get the better of me seeing as how I had wasted so much time on it already, I felt obliged to restart the entire game from the beginning only to discover that at 95% completion I was struck by yet another bug preventing me from entering a trap door and thus not allowing me the satisfaction of completion or all my trophies either.
In short, if you are fine sticking to the story mode and not overly concerned with trophies/achievements or just being able to collect everything in the game, then this is really a great game. If you are, give this one a miss, it will only lead to frustration.