Ars Technica has gone on record to say that they feel that Resistance 2 is better than Gears of War 2, which is a bold statement. The highly popular technology portal said the following in their review:
Even though the game’s campaign is a bit dry, the competitive multiplayer action and the addictive co-op will keep this game disk in PS3s for some time to come. Guerrilla Games is going to be hard-pressed to top this with Killzone 2, set to be released in early 2009. We’re willing to go on record as saying that this game is better than Gears of War 2 in many ways, and could very well be the best shooter of the year. Source


I think Ars Technica said that only because Resistance 2 is different from resistance 1. Resistance 2 is much better then its sequel. But gears of War 2 is as good and you can make the case better then Gears of War 1.
This does not mean that Resistance 2 is better then Gears of War 2. Gears of War 2 just had way too many expectations. I played Gears of War 2, and it is an awesome game.