If you've enjoyed the previous Harry Potter games, I suggest renting this one before buying. In the previous games real duels were few and far between. In the DH1 game, however, there is a fight around every corner. The sense of structure and story has been lost somewhat and replaced by an almost Call of Duty style gaming experience.
The game starts with the seven Harrys chase scene, where you learn to aim and cast spells while being chased by Death Eaters on brooms, and eventually Lord Voldemort. You have to stun Death Eaters, therefore making them fall from their brooms, to get past the first stage.
The game is very diffcult, even on easy. So far I've had to refer to walkthroughs three times to figure out what I was supposed to do to get past a level - most of the time it's not really that straight-forward and it's easy to, say, try to fight your way out when you should be going into stealth mode, dying multiple times over an extended period of time and simply getting frustrated.
You not only have to fight Death Eaters and Snatchers, but a range of other enemies - Acromantula (giant spiders) and Doxies (flying pixie-like creatures with extra arms, fur and poisonous fangs), I've found, are the easiest to fight. You'll face dragons (I must ask, why are there Hungarian Horntails in Britain? A Welsh Green would have been just fine), Dementors, Nagini, the horcrux inside the locket, and even inferi (human corpses controlled by dark magic, hardest for me to fight and also actually look like corpses).
Game situations include many muggle-born rescues, ambushes on Harry, and escape from various places, each often with a large army of Death Eaters and/or Snatchers, as well as dangerous magical creatures in many cases. Some parts can be scary, and they certainly got my adrenaline pumping. However, I did find the game enjoyable.