I suggest the following:

1. Disable physics at least for original map or all buildings.
Because players very often destroy buildings or all map just destroying bottom "layer".
2. Make players drown in water. Because no sense in islands and bridges if may make stairs or tunnel to water and just run across the water to another island.
3. Limit the transfer to another team(For example, like in Counter-Strike).
Because may easy go to another team and teamkilled teammates and destroy enemy buildings.

I hope, with these suggestions, game will be more interest.

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Sorry for my bad English:)