As i'm sure everyone already "knows", Bram Stoker's Dracula was theoretically very loosely based on Vlad III Draculea, the Impaler. This is his origin story, so there's really not that much surprising in terms of story. We know he's going to end up becoming the Dracula of legend, so this is definitely one of those "it's about the journey, not the destination" movies.
As just an action movie with special effects it was pretty good. The main characters were somewhat fleshed out, but often in a way with total disregard to actual human psychology, and most of their actions seemed to be based on stupid. Historically they picked a couple dramatic points from history and connected the dots with VERY wide brushstrokes for about the first quarter of the movie before going completely off the rails.
So here are some specific nitpicks
In real life Vlad _did_ was a hostage of the Turks as a child. Then after returning to rule Wallachia he got the name "Impaler" when fighting the Turks.
In the movie he was taken by the Turks, along with 999(?) other children, to fight in the Turkish army. Along with all the other children he was tortured and brainwashed as part of his training, and became known as the Impaler while fighting for them.
That's not a _huge_ change as far as movies go. However at the start of the movie (after the establishing narrative) he's the prince of Transylvania and is happily married and has a loving family that he plays with and tells bedtime stories to. All in all he seems _way_ too well adjusted and suffering from _way_ too little PTSD. And likewise after he goes full on vampire in front of his family they seem to be a _little_ too okay with that.
Later when conflict with the Turks has erupted, he goes to the cave of the original(?) vampire and makes a deal. By drinking his blood he gains the vampire's powers (and weaknesses) for three days. If he can resist drinking human blood for those three days he will become human again, otherwise he will become a vampire permanently.
That first night he slaughters the 1000 Turk soldiers who had invested his castle. After defeating them he vows that he will defeat the Turkish army within three days. Then the second night he... does nothing. He's evacuated the castle and sent the people to a nearby monastery and has to fend off one attack by the Turks on the refugees before they get there, but that's it. Then the third night he sits around in the monastery, until the main Turk army actually arrives at the monastery, less than an hour before sunrise, and starts their attack. At which point he desperately tried to defeat them all before the sun rises and he loses his powers.
There's a whole lot of WTF associated with this. First, if you've only got three days to finish off an army before your magical powers go away you go out and _find_ the army, you don't sit around hoping they'll show up before your time runs out.
Second, after the first 1000 are killed, or rather 999 so that there would be one left to relate what happened, word is taken back to the Turkish leader, who declares that they will march with 100,000 troops. First, if an army of 100,000 was able to get there in just two days, that army must have been camped _right_ at the border. In which case i'm pretty sure you just take your entire army with you. So announcing that you're taking 100,000 was probably just meant to let the audience know how big the army is.
But why did he have the army marching at night? That doesn't make any sense unless you're in a BIG hurry to get somewhere, and there was no reason he should have felt that rushed.
On top of that, after the first 1000 were defeated and then the raiding party was wiped out the Turk leader was told that the soldiers were afraid of Vlad. He then announces that they can't fear what they can't see and has the entire army blindfolded. Which just seems dumb for multiple reasons. I'm doubtful that they could actually march that way over anything but a wide smooth surface, and how many of those were there going through Transylvania at the time? Second, they're not scared of marching, they're scared of fighting Vlad, so if you're going to have them march blindfolded and then take off the blindfolds when they're going to fight it seems like you're doing it backward. Except for the part that having them fight blindfolded would be even stupider.
Finally (and this is the most spoilery bit) after the castle is attacked everyone is evacuated to the monastery. Then the monastery is attacked and it sure seems like one way or the other everyone there is killed. Yet after the war we see the kid getting crowned as the new prince and the castle is pristine and full of people. Where were all these people when everyone else was getting killed? Sure some of them could be visiting from other parts of the country that weren't part of the (very bloody but very short) war. However it seems like there really ought to be a dearth of nobles and soldiers.
 There have been arguments made that Bram Stoker didn't know as much about the original Vlad Draculea as people now assume, and/or that there were other historical and "modern" influences on the character. That's almost certainly true, however it's a bit of a stretch to argue that the character in the book who was named Dracula and came from Transylvania and fought the Turks had nothing at all to do with the historical person named Draculea who was born in Transylvania and ruled neighboring Wallachia and fought the Turks. (Though some people do try to imply that: http://io9.com/no-bram-stoker-did-not-model-dracula-on-vlad-the-impal-1648969679)
 His father was Vlad II Dracul, and apparently an "ea" is a diminutive in the local dialect, so Draculea meant "son of Dracul."