To sum it up, the situation is like this.
In Part 2, Kishi wanted Sasuke to have a huge edge against Naruto but didn't know how to considering how evenly matched they were at the end of Part 1. He decided to block Naruto from further expanding his arsenal of jutsus so that Sasuke could get a head start. Unfortunately
a)Naruto barely learning anything in spite of his many training arcs was annoyingly unbelievable for most of the readerbase and felt forced. Kishi tried to justify his training with a few repackaged Rasengans that did nothing new and never showed up again, inducing further hatred.
b)Kishi's longtime infatuation with the character grew exponentially and with the encouragement of Shonen Jump editors(the 'cool Bishounen' Sasuke was a major fanboy/girl favourite) he went overboard with powering the Uchiha hero up. Every time he faced a challenge, Kishi would casually grant him a new jutsu instead of having him work around it.
The net result of the above two events was that much of the fanbase(that didn't read Shonen Jump) became avid Sasuke haters. As for Naruto, they're not specifically bashing him but Kishimoto for his blatant attempts to deny Naruto any advancement compared to his wholly disparate treatment of Sasuke.
I'm not bashing Naruto either, so no need to bring up the usual 'jutsus do not a ninja make' defence.