I agree with the weathering of the tank in the water. Where the edge of the water touches the tank, you could add more rust, and some waterplants, lichens sort of things would add a lot to the realism. After all, it appears that this tank is in the water a looong time. Maybe some vertical rust and dust streaks, to simulate places where rain ran down after the tank broke down, would be nice. These streaks would be in an angle compared to the vertical lines of the tank, which would add a lot of realism. Just an idea

Also, it's quite odd that there's only grass growing in the turret, you can add some sort of small growth on other places of the tank, like muddy places, crevices,... Maybe that would be over the top, don't know.
Smoke is something I generally don't like in modelling, it hardly ever looks realistic. Your smoke is quite good, one of the better attempts I've seen on the net so far.
The water is awesome, and the weathering on the Panther is very good indeed.
This dio has a lot of potential, keep us updated!