Hi guys,
I would like your opinion on something. I'm about to start a project that involves to modify an existing First Person Shooter (or more generally fast-paced) game. I did a research on google and wikipedia and it seems to me that the only available and valid games are Quake engine based ones.
I was thinking that Quake 2/3 is already a dated game and I was wondering whether there is something out there equally valid and more representative of the new generations of games.

Do you have any suggestion?

Unreal is very easy to modify in terms of gameplay rules and mechanics. Certainly it's a great choice for experimenting with new multiplayer modes. The UDK is free and while you don't get access to the full source code, Unrealscript provides more than enough flexibility to the engine to probably handle what you have in mind.

-me

Cube Engine is pretty small and easy to modify.