Half-Life 2

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I checked the price of half life 2,in supermarkets;it's around 60 euros...(60 euros=78 dollars);in my opinion,it is very expensive for a game! the price of diablo 2 'battlechest' just after its release was about 45 euros,including the guides,but it was worth it.Maybe it's worth the price,I don't know,still,60 euros that's rather high a price.
I am interested to try it though:if it's that great,I could buy it;same for Doom 3,as I was told,'it's a great game'
So,I have some questions :
-what are the minimum requirements to play half life 2 ? (without freezing and no lag)
-is half life 2 a greater game than morrowind/doom 3/wow/neverwinter nights/sacred ? i ask this because I'd like to buy one game by the end of the year among these ones,and it has to be very good
-do you know where to watch a demo on the web?

Thanks,
Abramalin