Rozsival, Malik, and Poti got maligned for not much of a reason. They were what they were, and some of the fans got upset because Malik wasn't Chris Pronger, Rozsival wasn't Al MacInnis, and Poti wasn't gritty and didn't hit stuff even though he was OK in his own end, and good at moving the puck up ice.
Redden was in decline long before he got here, and the only thing that hid it was his ability to set up on the PP and feed Zdeno Chara one timers. No coincidence Redden's play fell off a cliff once Chara went to Boston, but of course that was attributed to "just a down year" and then two, before the Rangers paid him. Redden was absolutely a bust but that signing was terrible from the start.
Also felt Dan Boyle got a raw deal. He looked amazing his first few weeks with the team, but he was late 30s when they got him (another horrible signing) and aged quickly, but I never got the sense he didn't care. He was 38 when the Rangers got him. For comparison, another much maligned PP QB (Bruce Driver) was widely seen as over the hill when the Rangers got him but was only 33 and produced diminishing point totals each year up to his retirement at 35. No idea what the front office though Boyle would give them at 38.
Most undeservedly maligned was probably Marian Gaborik - for the numbers he put up and the way he was run out of town by the grit fellating section of the fanbase and Tortorella for being "soft and Euro" even though the guy was a scoring two way forward who came up defensively responsible in a Jacques Lemaire system and basically lived up to his contract every year that he wasn't battling injuries. And scoring a triple overtime goal with one good arm but being labeled a bust for a playoffs that he gutted through that probably cost him a significant portion of the rest of his career. Such BS the way he was treated.