Summary: The Mechromancer is a far superior character, IMO, but if you want to smash the ever-loving-hell out of everything in sight the Psycho should float your boat. Bottom line, what you see is what you get with this one. If you suspect you would not find playing a physical, "Og Smash!" kind of character fun, you probably won't like this guy. If you do (i.e.- Brick was your favorite in BL1 or something), you'll probably have a blast.
Summary: Borderlands DLC is similar to cash-grab, mobile techniques. Do you need this? Unless you have friends that you play with and run through the game without every getting bored, then grab it (during a sale) Otherwise, don't feed the machine. Make the publishers earn your money by producing REAL content.
Summary: It is what it is. A level cap increase with a little bit of add-on content added in there so you can replay the game a third time with the same character. Just beware - this is for hardcore gamers. If you don't like getting beat down over and over again because of the disparity between the readily available gear and the mob's increased toughness levels (I'm calling you out Rabid Stalkers!) then you might want to think twice.