NOTE: Everything was purple and black checkerboard for me. Have you packed the custom textures to your map?
Way too open
There's barely any cover and if there was cover it was a huge bland block. Since this is a mall you could make some shelves and then place these shelves in interesting places to break up sightlines (to not make snipers op like they currently are) and to give interesting advantages and routes for the players. Maybe have small flank route for scouts and spies. Maybe make some of the shelves fallen down to create a ramp, which then creates interesting highground.
The areas are wayy too big for what they should be. Slower classes will be really boring.
Also consider making the roof area a route to battle rather than a open fighting ground.
The layout is also pretty blocky
Adding some ramps or curved surfaces will definitely help
A bit cramped
While the main areas are huge the doorways and ramps are too small, and not that fun to go trough. Make them bigger and easier to go trough. This will make it a lot more fun to go trough these doors. IMPORTANT LESSON Please put the huge buildings in a 3D skybox. Them being inside the skybox is pretty bad for optimisation.
OTHER STUFF There's little gaps everywhere. These are pretty easy to seal up.
Your eye isn't really guided to the point, but you can still see them because theres no cover in this map. So when you add cover also add some arrows for both teams pointing where they should go.
I think this map has actually cool concepts and ideas. Also I think the brightful logos look cool.
Hope this feedback will help you improve. You can look up tutorials for some of the things I mentioned or just ask help in the TF2maps.net discord.