So, I return after a 2 year absence to find the game I loved 'WarLight' turned into this 'Warzone' and, it upsets me, I find it more difficult to use, the UI is even worse than the original and I can't even play on some maps, is it just me or has anyone else found it changed too much?

You should be able to play on the same maps. What do you mean you can't play on the same maps? Are you getting an error? If yes, what's the error? Is it taking too long to load? If yes, just wait. It'll load slow the forst time. Are you on iphone/android/chrome/Firefox?

You could switch to Flash to revert back to the old userface however you won't be able to use new features such as mods. Click on your name then click on switch to Flash.

the problem with not being able to play on the same maps is just that your level isn't high enough to unlock those maps.

You can still use the older UI by using the flash version and not the Unity version of the game. To change this you should click on your name in the top right of the screen and then "switch to flash" option.

On the name change, most of the community didn't agree with it but it's something the game creator has chosen himself.