First things first, get the map off megaupload. Put it on filefront or something. If you want it to get tested on
Gameday then you'll need it elsewhere.
I like this idea, it's funny watching the karts run around the track. It's like playing SSBB on the Mario Cart level.
Right, here's a few suggestions:
1.) Too much health.
Even though the heath packs are strategically placed, there needs to be less of them. Arena mode focuses more on the medic for heath rather then the items. Heath is placed mostly in the place of water to help counter pyros, who otherwise would be made too strong in arena mode.
2.) Spawns
RED and BLU's spawns are too close together, and they're very easily accessible. Without much cover between the two. Players can easily begin attacking each other immediately after the rounds starts. In most arena maps, there's a small quiet before the storm of the match really begins.
3.) The Karts cut corners.
This can easily be fixed by adding a few more path tracks. As it stands the Red Kart is a devious little machine that'll cut into the middle of the track and travel across the ramp. Also, I'd suggest you add some sort of overlay to show where the karts are traveling. Even in the Well maps, the train travels in a very easily identifiable, straight path, however there are still train tracks to show where the train will go. For this map, you might just want to add some sort of path, like a darkened part of the road where the karts have traveled.
4.)The Karts float.
Easy fix, just either lower your tracks or make sure the trains are set to be 0 units above the path_track.
5.)Ramps are too high/steep/skinny
This is a very common problem with both starting mapper and even intermediate mappers. While these ramps are smooth and can easily be scaled, they appear to be too high and two narrow. Keep in mind, the TF2 design is considerably larger then any other source game. In your map, the spawn rooms are actually a bit too large, which makes the ramp up to the second floor look very steep. If you use the dev wall textures, a good rule of thumb for a basic room size is one and a half blocks. As for the ramps, you also might want to widen them a bit, so it looks like more then one person can go up it at a time. Remember this: while the same team is passable through one another, spyies are not. Give them enough room to navigate around.
As for the second screenshot, this edge needs to be covered. You get stuck in the place shown since the ramp ends on both sides.
*pant* *pant*
Sorry for the long post, but I love death-trap based arena maps and this one seems like it could be a lot of fun. I'd love to see it on gameday some day.
EDIT: Forgot to say, Ubers are killed by the Kart. That was a fix since the train-stopping grief on Well.