I do like Willow through all the seasons. I think the only times I didn't like Willow was either when she was mouthing off to Tara or Giles or when she kept saying "GAY NOW". Not what she said, but how she said it.
Season 6 took everything they had been building up since season 1 and pushed it into overdrive. Controlling Willow had always been there but so had insecure Willow. Sure, dating Oz and Tara made it seem like Willow was more confident and outgoing but that doesn't mean her insecurities went away and it probably, in fact, created new insecurities. However, because of how much screen time is given, we don't really get to see Willow still have these insecurities and to us it looks as though she's different from seasons 1-3. She really isn't however, nothing about seasons 1-3 Willow left, they just got pushed to the side for her romantic storyline or her magic storyline. When you take an insecure person and give them something that makes them not feel so much like a waste of space, bad things tend to happen. Hence, the end of season 6.
Season 7 Willow is her insecurities now being front and center all the time and I take it as years of repression trying to not let those insecurities show. She was not doing magic as heavily and so what made her feel powerful wasn't really there and hence insecure land. Had Willow continued to do magic in a responsible way (which she wouldn't hear of because she felt it would already be too much), she probably would have been more confident.
Also, I sometimes find it hard to grasp that Willow moved on from Tara too fast. I mean, if we count episodes, Willow moved on from Oz faster than she moved on from Tara, yet I don't hear a lot of people being upset with that. Willow didn't end up kissing Kennedy 5 episodes later from Tara's death, so I don't understand the "She moved on too quickly" mentality. Tara was with Willow throughout the entire season. Even when she began dating Kennedy, their first kiss it was all about Tara and how much Willow loved Tara. Sure, a breakup is different from death, but I'm assuming a lot of time has gone by before she even thinks about kissing Kennedy. Even longer to even think about sex.