1. Dana and Dinah are annoying. They also don't seem to have much personality, and only really exist to get the gang to follow them out of the Great Valley (something that the gang probably would have done anyway
Agreed. LBT 6 would be as good as 5 or better if they hadn't been there. But they needed Saurus Rock to break somehow and the writers were too lazy to find a way just using the gang. (Which is why I think us members here would make good writers

)
2. The animation quality seems worse than in other sequels. Maybe Universal outsourced to a different studio for this one.
I belive it was the same as movie 5. Really, I hated the colors of this movie and 5 compared to 2-4. The colors in those movies were mainly beautiful greens and blues and grays, whereas 5 had more yellows and chartruses, and 6 had more reds. But that's ok, seeing as it showed them wanting to do something different. As I said before, though, 6 being a disapointment didn't seem too unexpected after 5, which felt like a cross between the earlier sequels and this one, quality wise.
3. The songs. I just don't think the country/western sound fits in the LBT universe. (Okay, "On your own", or whatever that song is called, is not so bad).
The first I fast forwarded through as a kid (I'd been fast forwarding it 5 minutes before it even started, seeing as I liked messing with the VCR); when I watched it again back in summer 2011 I remember sorta liking it...sorta like how some people may have a "guilty pleasure" for songs like "Baby one more time". But i definitely considered it inferior to other songs the series had gotten.
The second I LOVED as a kid; at least the first verse; I'm not sure if I liked Spike's part really. But I thought it was epic and watched it until I started seeing it for it's flaws (Ducky's line about getting a "boo-boo" sounded really whiny, I thought) and soon forgot about it. But then when I heard it on that youtube medley of songs, I was suddenly hooked and listened to it again and it was like rediscovering it! It was definitely a high point of the movie, and one of the few great moments between just our gang WITHOUT THE TWINS. Really, the twins got in the way of the gang having so many great moments together, like in 5, which is why I like it over this one. Anyways about this song I still see it for it's flaws...but it's great and one of the last "Great" songs the series got. What genre is it, BTW? I've heard someone say it's swing, but it could also be called jazz or blues...also, do you think it would sound as good without Spike's vocals?
The last one I'd pretty much forgotten about by the time I rediscovered LBT 2 years ago, and I like it, but the more I hear it, I see it's flaws.I love the piano riff, though, espicially before the last verse. I get the visual of being alone on a deserted school campus on a sunny day, almost.
Also, I'm pretty sure all of the sequels are traditionally animated, and from what I gather, 2-6 were inked and painted on cels, while 7-13 were digitally inked and painted.
I miss the animation of 2-6!
All in all, while not as good as the first 5, at the end of a long day this one is definitely fun. The score was beautiful, and it was a fine way to end the LBT of the 90's. I hear it was actually originally going to be the last one. Is that the reason that we didn't get one in 1999?
Oh, and after the credits, watch the universal logo. It's...different