You're making an assumption (they don't say anything about that), most of the people that mentioned LotSB loved the fight with Tela Vasir more than anything else. Further, initial reviews usually gravitate towards such things, they quiver the nostaglia glands. It's far better to get a sense of how people feel after the glamour is gone, and they look at things with a clear mind.
When I first played Old World Blues in Fallout: New Vegas, I was stunned, it was a complete tonal shift that shocked me, and I came out of it with a big "huh?" After I played it again a few months later, I started thinking "Yeah, this is hilarious, it's funny." Likewise, once people stopped thinking "OMG, it's nice to have Liara back" and "Ooh, Tela Vasir fighting is fun", they could stop and say: "Hey, wait a sec, she's got my charred burned armor as a trophy. Cree-py" and "Hey, the third party member doesn't talk at all, despite it being Garrus or Tali. What gives?"
More to the point, people are still complaining about it now, and, like it or not, the complaints exist and have merit. Instead of making the argument that "Oh, they're just haters who are obsessed", accept that Liara was forced as a bestie, that she got far too much screen time to justify her flaws, and move on.
Yeah, a few haters complain about it now while a vast majority still considers Lair of the Shadow Broker as the best Mass Effect 2 DLC, just like most professional reviewers. And that has very little to do with the Vasir fight. Banter, graphics and level design all took up a step up in quality.
And when the developers describe Liara as a fan-favorite, as a beloved character, the face of the franchise and one of the most recognizable character of Mass Effect I tend to believe them. Together with fan polls all over the internet and Bioware's own statistics you'll get a rather comprehensive picture. I'd say the obsessed haters should just accept that they are a small minority, and move on.
Chris Priestly said, for example, in one thread about Citadel DLC, in reference to someone noting Liara always seemingly taking precedence over other LI: "Ok. Fair points. Certainly in the past Liara has played a large role (LotS for example), but for that reason she is featured a little more prominantly in this trailer. She has been used as a face for the game and is easily recognized by casual ME fans as a character in the series. Not everyone would know who Traynor, Grunt or even Wrex woudl be, yes hardcore fans absolutely, but casual fans, less so."