Warning: SPOILERS AHEAD
First of all Deathly Hallows is amazing, and to the few fans who disliked it, they are missing JKR's point of view.
Second, Deathly Hallows is dark, very dark. Not only are their constant fights and ambushes, but people close to your heart die. Remus, Tonks, Dobby, Fred, Snape and Moody. Once you finish reading and everything sinks in, the sadness of losing them will be just as heavy in your heart as the happiness of Voldemort's death.
Deathly Hallows is very well assembled. JKR has managed to unite almost every loose end. It is also very quick. DH begins with an escape from Privet Drive to the Burrow. This results in Moody's death and George losing an ear. Fred and George's humour is evident even here, where George remarks that he is saint-like (holey!). After a short hiatus of Bill and Fleur's wedding ( which nevertheless leads Harry on the path to the Deathly Hallows ), the action begins again. Harry, Ron and Hermione have to run away and try and destroy all the Horcruxes. What I really liked here was the friendship, yet the palpable strain on it due to disappointment.
The Deathly Hallows are a collection of three objects (Harry's Invisibility Cloak, the Resurrection Stone (Gaunt's ring) and the Elder wand) which give the owner control over Death, although this concept is never really totally used.
The grand finale is at Hogwarts, where Harry, Ron and Hermione arrive to find the final Horcrux. Hogwarts has already revolted with an underground movement lead by Neville Longbottom and other DA members. The Room of Requirement, thought to be introduced merely as a location, assumes prime importance in the seventh book. Voldemort leads the assault (but doesn't actually fight) with Death Eaters, Aragog's descendants, Giants and his fear. Remus Lupin, Nymphadora Tonks and Fred Weasley die during the battle.
Snape gives his memories to Harry in his dying moments, explaining his connection with Lily and whose side he is really on. The memories also reveal that Harry has to sacrifice himself.
Deathly Hallows ends with a strange union between the living and the dead when Harry goes to the nether world to commune with Dumbledore, yet remains alive, tied to Earth by his blood in Voldemort's veins.
The secrets of the Elder wand and its ownership finally lead to the downfall of Voldemort.
When you finish the book an overwhelming sense of peace permeates you, yet gloom that this is the end of one of the greatest stories of all time. You also have a new perspective of Dumbledore, and his imperfections.
The Epilogue on the other hand is bad, plain bad and I expected better from Rowling. She merely completes the circle by depicting Harry and Ginny's kids getting on the Hogwarts Express nineteen years later. I was expecting something about what all the main characters did for a living, what was the state of the wizarding world, the attitude towards lesser beings. I would also have liked a bit of the immediate aftermath of the end of Voldemort, I mean there has to be a lot of cleaning up. Harry and the Dursleys meeting again would have helped.
Considering that this was the last book a decent 700-750 pages would be better, perhaps she could expand more on the fifty who died, and what the other members of the Order where doing when the trio were zooming along the countryside. A bit of contact with their friends could have really helped them.