Just Cause 2 is one of the few games I can think of where cheating actually makes it better. I don't have any kind of god mode mods for it (that would make it TOO easy), but I do have an infinite ammo mod, which preserves just the right amount of difficulty. I also have a flying/superhero mod, which makes the game WAY more fun. Why grapple/parachute all the way across the island when you can FLY LIKE FUCKING SUPERMAN?! With that mod turned on, it becomes the best superhero game never made (the mod community is actually working on an Iron Man total conversion mod). Another game that gets better with cheating is JK2: Jedi Outcast. God mode + edited sabercolor + dismemberment cheat = what Force Unleashed should have been.
As for Half-Life 2 cheating, I only used god mode for about 5 minutes total near the end, in a really rough patch.