One thing for me is that it feels less like a sim, and more like a game.
And no, I'm not comparing it to T2. I liked T2, but mostly for the scripting changes. I played T2 mostly just 'cause it was Tribes.
T1, though, was built by a team that were flight sim makers at heart...and it showed. I've always been a sim kind of guy...I owned every single game ever published by Microprose, for instance. T1 felt to me like a "personal armor simulator." It felt more immersive for me...I was in the Tribes universe, I was right there on Raindance and Rollercoaster and Stonehenge.
T:V feels really...artificial in comparison. It's pretty, but not in a gritty enough way...everything has that kind of, I dunno, kid's toy look to it.
A lot of it, I think, has to do with the maps and the, uh, cutesy-cartoony UT2k4 engine. The maps are just too small, I don't get that sense of being in a real place like I did in T1, that sense of exploration when you played a map for the first time. Instead I feel like I'm in a sports arena.
LabRat said something in the GG forums that resonated a bit with me: Planetside feels more like Tribes than T:V does. As much as I dislike SOE and have issues with Planetside, there's truth in what he says. It's almost like someone took Tribes and split it in two...the strategy, warfare, teamwork half was given to Planetside, and the "sports" half was given to T:V.
There are a lot of little things I really like about T:V...such as the empty disc launcher clip animation which was just such a great decision. The game is full of nice little touches like that, it's obvious a lot of care went into it. But there seems to be something missing. Hopefully it's just the maps, although if it's true we're only getting another 6 at release...I dunno.
Like the others here, I really want to like this game...I just wish I didn't have to try so hard.