[quote name='meta1militia']yes, play 2 first. 2 will keep you busy for a long time, and you wont want to play 2 after you play 3. 3 has a little less to do, however 3 has an amazing leap in graphics, framerate, and physics (in a good way, not a bad way like gta4)[/QUOTE]
I don't entirely agree (especially about GTA's physics!), I had no problems going back to SR2 after 3. 3 certainly has a lot of improvements and new activities, but SR2 has its own stuff that SR3 doesn't have which I enjoyed quite a bit like fight club and security detail. I also generally preferred SR2's world, and SR2 has Evil Cars and Low Gravity cheat codes that when combined make for a very fun diversion. Probably the only thing I didn't like about regressing from 3 to 2 was SR2's story: your character is such a douchebag, wheras in 3 you're a pretty likable character. In short: I don't think you need to play the games in order, and I don't really think SR2 was made obsolete by SR3. You can probably ignore SR1 entirely though, pretty mediocre IMO.