Looks like Team17 decided to revert back to the times of Worms3D, where they used XOM files there.

I don't quite like the graphics of the game though, the worms look too "shiny" and seemed to have lost its original pinkish colour.

I must admit that gameplay doesn't seem smooth enough. I prefer Worms 4 Style, it just seems more natural. Mouse sensitivity is kinda rusty (maybe it's only me). I'll play and explore the game more in next few days, so I'll know more. Good thing is that you can progress and play ranked games. Also, I like Worms 3D campaign. Anyway, worms ultimate mayhem is like high definition mod (expansion) for Worms 4. Nothing more, nothing less. They should have followed .xan format, because that's the only thing that kept so many of us playing Worms 4 still. Because it was tweakable.

I'm sure in time someone will come up with a way to mod the .xom files.

I just might be on a good way to unlock .xom for editing Will report later today results.

Looks like AlexBond has a start on map editing for WUM maps.
http://forum.team17.com/showthread.php?t=49562

Also, you never did report.