As a PS3 owner, there are a lot of reasons not to buy Resistance 2.
The largest reasons being how CODwaw came out 1 week afterwards, and the knowledge that Killzone 2 is coming out in February.
That is 3 very good FPS's in a matter of a few months. Do I need all that?
All I know is that some of my friends have CODWaW and want me to get it also, (this is arguably the best COD out there for a year until IW's next effort)... and that is a big reason to buy that game.
And there is no way in hell I will not buy Killzone Day 1. That is THE shooter, until Christmas 09, (and even then it may still hold up)
Point is, regardless of how good Resistance may be, I really want the other two games as well.
The reality of the situation is I do not own any of the above mentioned games, due to a busy schedule and lack of money.
Despite the logic I have blasted into your faces above, I have asked for Resistance 2 for Christmas, and as I previously stated- will buy Killzone immediately upon release.
So for me , that just leaves COD trailing... until I can find a reason to justify buying it myself, which will probably happen over Christmas break.
And since I am incoherently rambling at this point, that will create quite a few games to play over Christmas for me, including Gears 2, Fallout 3, Resistance 2, and CODWaW, and some LBP as well.
There are many reasons not to buy Resistance 2 now.. but no justifiable reasons not to buy it sometime in the future.