I watched Insurrection this morning over breakfast and really enjoyed it. It's very flawed but still a good movie and actually sets out to tell a science-fiction story unlike most of the Trek films. I've enjoyed it more than The Search for Spock, The Voyage Home, The Final Frontier and Generations during this marathon. Might also rank it above First Contact too as it resembles Star Trek a lot more but I thought First Contact was better structured as a movie.
I think people tend to be WAY too lenient on the TOS movies. Nichols and Takei are awful in them (Though Koenig is weirdly great!) and the crew seem ridiculously lightweight and cosey compared to how they were in the series. I still enjoy them all but I'd definitely say First Contact and Insurrection are better than a good chunk of them.