My personal opinion: I thought 3 was fantastic. Not quite as magical as the first one - nothing ever will be - but far more enjoyable than 2, which to me is easily the least enjoyable of all of them. Just not quite big on the new characters in that, from Jesse and the Prospector to the creepy toy collector. 3 was great though, Lotso was a fantastic villain. 3 stunned me with how good it was after waiting so long, and I hope 4 does the same. I never thought the plots were unnecessary or showed Pixar reaching just to extend the life of the franchise.
I am curious about what 4's plot will be though considering the end of 3 neatly wrapped everything up. I heard something about Bo Peep being in this, like Woody setting off to rescue her - was she in 3? I honestly can't remember.