I reckon for say... a grinding game (mmorpg for most of the part) it makes you feel satisfied with all the hours you have wasted smacking around monsters.
thats until someone beats you ovcourse.
so Im about 50-50 with PvP in online games.
for those who dont know what it is.
heres an example, a tournemant (snipits from) from FlyFF showing you some elements of PvP.