I guess we all watched this great series and personally I lived inside it, so I can easily get you 10 points that makes this great series the best fantasy series of all time.
I don't see any other fantasy series having sports in it and such a major sport, too.
9- Voldemort's arrogance
it shows us that Evil can't be perfect it will always have flaws.
8- Importance of friendship
Harry would never have been able to beat Voldemort without his friends, and he needed them in every single task in each movie.
7- Each character's death had a meaning
Let's take them one by one:
Cedric Diggory: innocent people die everyday
Sirius Black: Harry will suffer the lack of parent/guardian
Albus Dumbledore: even when the leader is gone we have to keep fighting
Hedwig: The end of Harry's childhood
Alastor Moody: even the toughest people will die
Dobby: the loyalty and heroic death of even the smallest creatures make us cry for days
Fred Weasely: the great losses of war; even the people we can never imagine die
Remus Lupin & Nymphadora Tonks: the orphanage results of war
Collin Creevy: heroes can be so young and innocent
Severus Snape: you can always change your ways
Tom Riddle, Lord Voldemort: evil will always fall
6- The connection between events in all 7 parts
All of them led to the Battle of Hogwarts and the resurrection of Lord Voldemort.
5- Ron and Hermione's love story
We all knew from the beginning that they would end up together but the details that led to this were quite impressive and interesting.
4- Applying the three brothers story as Voldemort, Snape and Harry
They didn't own the Deathly Hallows each but they were just like them.
3- Nobody has ever gone this far in Magic
The magic in this series was very detailed and accurate: the variety of spells, hexes, jinxes and magical creatures was one of the best things in the whole series.
2- The plot twist of Severus Snape
Some people consider this as their favorite moment in the series and no one can deny that it was amazing and changed all of our feelings toward him.
1- Living with the characters through all their life stages
This is my favorite thing about the whole series and I think it's what made it special. We lived with Harry and the characters in their late childhood and we saw passion and excitement; we lived with them when they were teens and we saw the disturbance and the adventure spirit and bravery, and we lived with them as adults and we saw how they were great parents.
I will be glad to know your opinions.