For me the trouble with Six is not that he wasn’t like the other Doctors, it was that he seemed to take all the somewhat negative aspects of them and dial it up to 11 with no real redeeming features.
That's an unfair assessment of the Sixth Doctor because--like all Doctors--he was still a champion of good when all was said and done. Sure, he had a rough start but that was by design. Towards the end of his run, the Sixth Doctor had mellowed out quite a lot (I think that was also by design).
I think the Sixth Doctor was a reminder to viewers that he was an alien, a Time Lord, and this version of the Doctor had a more objective view towards humans than previous incarnations. That may come across as arrogant to some, but it's a trait that's common to every incarnation of the Doctor to varying degrees. With the Sixth Doctor, it was sort of amplified by the fact he didn't care what people thought of him too much, but even this was toned down over time with Peri and Mel.