It has it's flaws, but it has it's good points as well.
Harry Potter and the Philosopher's Stone – or Sorcerer's Stone if you live in the US – was the first in the series, telling the tale of Harry's discovery of the world of magic, as well as his first adventure in Hogwarts School of Witchcraft and Wizardry. This game follows the plot of the book/movie fairly loosely, in that quite a few noticeable events from the book and movie occur, but also a fair amount of original stuff happens too. I don't really have an issue with mild deviation, so long as they don't completely change the plot, and they didn't.
The gameplay mostly consists of Harry exploring Hogwarts and attending lessons. Hogwarts Castle is reasonably sizable and it has quite a few things hidden around, so exploring every nook and cranny is essential if you want to find everything there is to be found. You cannot access all of the castle straight away, you need to do certain things in one area of the castle before you unlock another area. Yes, you can roam around the sections of the castle of your own free will but you will not be able to move the story forward. Harry doesn't just explore the castle via running about, he can also climb and jump so there are slight platforming elements found in this game, which is enjoyable and the controls work well. The fact that you could not access the whole castle from the start also prevents the game from becoming stale too quickly, as each area you enter is fresh.
As I mentioned before, there are quite a few things to collect in the castle, some of which is hidden, usually behind slim bookcases and stone slabs. For one, each section of the castle has a portrait with a prize hidden behind it, but you can't get into these without a password. Where do you get the password? By trading Bertie Bott's Every-Flavour Beans to the Weasley twins. These beans are scattered around the castle and collecting a certain number of a certain colour will net you the passwords, and those prizes, which do come in handy in some aspects of the game.
You can also collect Famous Witches & Wizards cards, which upon collecting them all gives you access to the secret ending of the story. Most of these are hidden or require you to complete a mini-game, but sometimes you'll get a few in the course of the story when you complete certain tasks. You can then view them in your portfolio.
Also scattered around the castle are Chocolate Frogs and Wiggenweld Potions, both of which serve the purpose of healing any damage you've taken. Your health is displayed in the lightning symbol on the top of the screen and when it's empty, you die, which doesn't happen all that often due to the level of difficulty in the game. Chocolate Frogs will only heal a small portion of your health, but Wiggenweld Potions will completely heal you, however there are less of them scattered around.
As you can probably expect, Harry will have a few spells in his arsenal, five to be precise, and you'll learn them all throughout the course of the game by attending lessons. In each of the lessons you attend, you'll find yourself needing to jump across platforms in order to reach your lesson on time. Fail to reach your lesson on time and you lose House Points, which I'll get into in a moment.
In the lessons you'll find yourself tapping a button combination in order to learn spells. This is basic for the most part, but I found that there is a slight issue with timing. Namely that you have to hit the button just before the curser gets to it on screen, or else you miss that button and you'll have to spend longer doing this until you get the combination right a certain number of times. However, this isn't a huge problem as it's very easy to get used to. After that, you get to cast the spell and be on your merry way.
Flipendo is the first spell you learn and the only one you don't learn in a classroom; it's also the most important spell you'll learn since you'll use it to attack enemies among other things all throughout the game. Wingardium Leviosa enables you to levitate items, Incendio is for burning certain plants, Verdimilious makes dark matter turn into platforms temporarily and Abifors transfigures giant bird statues into tiny birds. Each spell has different means of casting; while Wingardium Leviosa and Verdimilious don't require any extra actions to make them work, Incendio and Abifors require you to hit a button combination in a short period of time. I found Incendio in particular to be quite annoying to cast since the slight timing issue from the classroom affects casting this spell too, and it's even more annoying. Again, you have to hit the button slightly before it reaches the small circle as opposed to when it reaches it. The button icon moves so quickly that you have to get the timing right. Mess up and the button combo restarts, and you only have a set time to hit them all in. You can get used to it but I still found it annoying and occasionally frustrating.
As I mentioned before, you can earn house points, usually by completing certain tasks that occur in the story but also by doing odd little bits about the castle - like levitating a candle to a table - or tackling mini-games. Mini-games are usually hidden around the castle and they're relatively easy to beat, though are a tad on the tedious side. House Points don't really mean much in any case.
Occasionally you'll fight a boss, but not very often, however these bosses were pretty enjoyable to fight anyway and considering the plot I can understand why there wasn't more of them.
Occasionally you'll be able to partake in flying throughout the game – in flying lessons and in the sport known as Quidditch. Here you'll be able to jump on a broomstick and take to the skies. How? By flying through rings. While that sounds quite boring that really isn't the biggest problem – the controls, while not terrible, do feel a little bit loose, particularly on sharper turns. In a Quidditch match you'll find yourself flying through a series of hoops until you can catch the Golden Snitch. When it comes to doing that, you have to catch it when it comes to your hand in a bar, but once again there is a slight timing issue here, and you only have a certain amount of time to catch the Snitch in. I don't remember ever losing a Quidditch match despite these problems though – because it's insanely easy. There's a separate Quidditch mode in the game that lets you play Quidditch to your heart's content but... nothing changes in this mode barring the scenery on occasion so it gets boring really quickly.
The game is quite straightforward and easy but considering this was made with children in mind, that's fair enough. It's also quite a short game and once you beat it, that's it. No returning to Hogwarts unless it's in a new game. Yeah, even if you've missed some prizes or Famous Witches & Wizards cards, there's no returning. I would have liked to have been able to collect everything I missed, but it seems like I could only have done that in the game.
The graphics look okay, bearing in mind that it's a PS1 game. Some of the character's faces look like they're squashed and some of them, like Harry's, don't. The scenery looks nice and fitting for how I imagined Hogwarts in the books to look like before I saw the films. The sound is also pretty good. Background music is used only where it's appropriate and not all the time and I like that. The music that is used is pretty good and quickly becomes memorable. The voice-acting is okay; it sounds like they only casted one voice to cover all the boys, and one voice to cover all the girls (of which there's only one or two and that does include Hermione). However, it's not something I let bother me, at least the boys genuinely sound like young boys and the acting itself is not too bad. The other characters sound okay, though not necessarily the same as their movie counterparts. I do have one thing to say though... that squeaking sound effect when running across certain floors? Yeah, it's annoying.
In conclusion, Harry Potter and the Philosopher's Stone for the PS1 isn't a bad game, though it's not a spectacular one. Potter fans like myself will probably enjoy it a lot more than non-Potter fans, even with it's flaws. I certainly enjoyed this one more than some of the later Harry Potter games. So with that being said, I think it's worth looking into especially if you're a Harry Potter fan or know somebody who is one. If you don't like Harry Potter, then I don't think this game will change your mind.