I love mods, aslong as they change/add elements of gameplay (every thing is better if you put more crap in it.) or if they change the map lay out, other.
Sword... From Mac.clanhalo.net IS THE BEST MODDER EVER, with his Island mod (Haven't played Halo:Combat Evolved Demo in ages though), the basic run down of the mod is that it replaces Blood Gulch with the silent cartogrepher map, for multiplayer as well as spawned drivable pelcans and unlike most modders for the demo actually remembered to put the locations for the tanks and ghosts as well as odd balls and king of the hill spots, if you wanted to try out another game type besides ctf or slayer. (I AM NOT RAMBLING ABOUT HALO, I AM RAMBLING ABOUT A MOD FOR IT.)
Another demo with good mods was Battle Field 1942's demo, I won't go into detail there but the demo was so popular that the server had to have it that you were a member to play it. (I think the server was gamespy, or was it gamespot (One of those)) Which I found rediculous... I MEAN PAYING FOR A DEMO??? WHAT IS WITH THAT?