Well let me start by saying don't waste your money on Demon's Souls unless you have an incredibly large amount of patience and a lot of free time on your hands. Demon's Souls is a very good game, but is probably the hardest I've ever played in all my years of gaming.

The hardest thing about this game is probably the lack of checkpoints. Everytime you die you're sent back to the beginning of the area and have lost all the souls (currency) you earned. You have one chance to make it back to where you were killed to regain these souls, but otherwise they are lost forever. This can lead to a lot of time wasted  and a lot of souls lost. Also, you have a stamina bar, meaning you can't just mash buttons or block for the entire time. When your stamina is gone you have to wait for it to regenerate before you can attack, run, or even use your shield.  This can lead to a lot of chances for enemies to hit you while you're down. And as you die more and more the enemies become even MORE powerful. With all these odds stacked against you this game can easily keep you stuck long enough on one area to lose interest. 

But even though this game is infuriatingly difficult, every time you defeat a giant boss or get past the level that seemed impossible your spirits are lifted and make you want to play on.  The thrill of reaching the goal you've tried for hours to achieve is priceless. This game's lows are very low, but its highs are very high.

The online aspect of this game is interesting as well. There are chances to work with people to help you regain strength and earn souls, but there is also a way for you to invade another players world and attempt to defeat them to gain strength and souls as well. This can lead to great team work, allowing everyone to benefit, or it can lead to great pains when you have to worry about even more in a level that already seemed impossible.

I think Demon's Souls is a great game, but the nearly impossible levels can make it slightly tiring. Any hardcore gamers will love this game, but I personally think the incredible challenge decreases the fun that this game has to offer. However, this game is still incredibly fun and I would reccomend to anyone who wanted a challenge.