To be honest, I think you can just jump in this season. There's some Chloe stuff that probably makes a little more sense if you watched last season, but honestly I think it can stand alone pretty well. I mean, I watched the last three seasons, but they haven't made much of an impression on me, except that Lois got really awesome, Lex left, Tess came as his "replacement" (though she is more of a good guy than he was at the end, and also quite awesome as a character herself), and Oliver Queen plays a fairly big role.