Boring, repetitive, frustrating. You do the math.
Harry Potter and the Half-Blood Prince starts you off at the Weasley's house to learn the basics of the game. The first spell you'll learn is Wingardium Leviosa, or in other words how to make objects levitate. Unfortunately there are only a couple of sequences in the game at most where you'll be forced to use this, making the tutorial of it relatively useless. The second tutorial is attempting to catch the infamous snitch (i.e. Quidditch). All you have to do is fly through circles until you catch the snitch to end the sequence. This makes it extremely boring during actual Quidditch matches when all you'll be doing is flying through floating circles without even an opposing Seeker.
Once you beat the tutorials, the movie's story will unfold courtesy of poorly constructed cutscenes, such as Malfoy discovering Harry spying on him on the train to Hogwarts. The game does a decent job of replicating the movie's plot, but for those who haven't seen the film, you'll probably be a bit confused. You'll see Harry and Dumbledore talk about Voldemort while he was still attending Hogwarts, and Slughorn's late-night party. However, there are few actual story missions to take part in, making the plot here feel more like a trivial afterthought. Most of the time you'll just be randomly dueling either Crab or Goyle or sometimes both in various parts of Hogwarts, and while this isn't much fun to begin with, having to do it multiple times throughout the game becomes extremely agitating.
Speaking of Hogwarts, it's actually pretty fun to explore it. The sheer size of the environment is impressive, but that means it'll take some time to know where you're going on your own. Thankfully by selecting a destination on the pause menu, you'll automatically summon Nearly-Headless Nick to escort you to that location. I think they did a great job of creating Hogwarts, as it matches up very well to the movie. However, it's odd how a portrait on the wall appears to be the main entrance into Hogwarts instead of huge doors. And what happened to the Entrance Hall? It seems to have completely disappeared. A lot of the time you'll take shortcuts through various portraits found in Hogwarts. Unfortunately the controls are mediocre at best, ruining part of the experience of exploring Hogwarts. You have to hold down RT while moving the RS around to move the camera around. But what's with holding down RT? You can sprint by holding down LT, which is pretty stupid in the first place, but not being able to turn while sprinting is flat-out retarded. Also, if you bump into someone while sprinting, you dive down onto the ground and I swear it literally takes around 10 whole seconds to get back up. This is simply unacceptable.
There are three main things you'll be doing throughout the entire game: Making potions, dueling people and playing Qudditch. I already described how Quidditch works, but I'll just say once again how disappointing it is just to fly through circles. You can't even fly freely around the field; no, instead you're on a linear path that you can't strafe from, making it all the more disappointing. Potion making is fairly simple early on but later it proves itself to be quite the nuisance. You have a set amount of time to pour different ingredients into a potion pot. It becomes more complicated when you have to stir or heat the pot to match a certain color, or to shake a bottle before pouring it so that it doesn't spill. Dueling is actually somewhat fun. You cast spells by moving the left and right sticks in various directions. I don't get why you couldn't just hit either X, A, Y, or B to cast spells instead. You can also dodge an opponent's attack by pressing either RT or LT, depending on which way you want to dodge. The most annoying factor by far in dueling is when you get knocked down. Despite how many times you cast Stupify or the sort on your opponent, one lucky spell can knock you down, providing easy access for spells to hit you. You can participate in various "clubs," with these three activities in them, but why would you want to after doing it so much in the story?
The visuals aren't exactly up-to-date, either. Harry and Ron's faces look good, but Hermionie's and everyone else's just look god awful. Cutscenes, like I said before, look very poor at best. In-game visuals actually look pretty good, with nice details and lighting effects of Hogwarts. However the lip-syncing is simply unforgivable. When characters talk, their lips sometimes don't even move at all. The audio department is even worse. Aside from Harry, Ron and Hermionie, everyone else in the whole game sounds like they've been hung over for two days. Overall, Harry Potter and the Half-Blood Prince is a VERY mediocre game. The only real saving grace is actual concept of exploring Hogwarts. Only get this game if you're a die-hard fan of this overly-long series or if you want some easy achievements. My advice in general is to skip this mediocre game and the epic failure of a movie its based on.