SR3 was the first one I played, and I played SR4 almost immediately after that I think. Then I tried to play SR2, but I thought it was absolutely dreadful.
I had to turn off all the advanced lighting features like ambient occlusion and HDR, because every object looked like it was smothered in grease and there was a blurriness/fogginess over everything. The visuals were greatly improved once I turned those things off, but then I'm playing a game from the 360/PS3 generation released in 2008 that looks like it's from four years ago on the previous gen. I'm not a graphics whore, but for 2008 it was pretty bad. Lighting isn't that hard to get right, and without it everything looked "basic" - I remember being in a cave at one point and there was no darkness to it at all because I'd turned the advanced lighting off. The cave might as well have had the sun inside of it, everything was perfectly illuminated.
Then, the pop-in was the worst I've ever seen. I could stand in place and rotate the camera, and I would see things disappear and new things appear, and not at a very long distance either - things only a few metres away from my character would spawn/despawn just from doing this. It was especially annoying when I would be driving and see a car I wanted - slamming on the handbrake and turning around wouldn't be fast enough before that vehicle would vanish.
The controls were pretty unintuitive aswell. In menus I was allowed to use the up/down arrows to move my selection vertically, but I couldn't use the left/right arrows to move the selection horizontally - I was forced to use Shift and CTRL. Any attempt to remap these controls to the arrow keys to make the menus more intuitive would have resulted in sprint/crouch/etc controls being remapped to the arrow keys too, so I couldn't do anything. Walking around felt clunky because of the way the character turned. Again, didn't feel like a game released in 2008.
Even the shooting sucked. Fine aim being a toggle instead of holding the button down might have been something I got used to had I played the game more, but I never got used to it in the couple of sessions I played. Also every time I switched from being unarmed to holding a gun, the very first shot would either be delayed 1-2 seconds (but the game wasn't slowed or frozen at all), or the first shot would simply not go off. Also the aiming felt more like the overly-simplified GTA III controls than it did something more refined that came out the same time it did, like GTA IV. GTA III was released 7 years prior.
Finally, as mentioned before, this game is from 2008 and was competing with games like GTA IV, which is just 100 times better in every imaginable way - gameplay, controls, mechanics, graphics, everything. Infact even comparing SR2 to San Andreas it comes up short in every way except for the graphics, and even then I'd probably still give the nod to SA because for its day and that generation, it was quite good (for comparison GTA III was on the same gen, but SA is still an improvement) whereas SR2 was bad even for its time. GTA SA didn't have pop-in even remotely as horrible as that of SR2, and it was four years older and on a previous gen console.
I wanted to play it for the story, to see what events transpired before SR3, but I just couldn't get past all this stuff or enjoy the gameplay at all, and wanting to see the story wasn't enough of an incentive to tolerate these problems. So I gave up.