Is installing mods easy? Should I even bother?

It heavily depends on the game itself. For mod friendly games, intalling a mod usually just means copying the mods contents to a folder called "mods" or something inside the main game's folder; then, usually, when you start the game, you have the option of either playing the main game or the installed mods (as I remember, The Witcher works like this). This is the more common situation. For a few other games, it might mean replacing some files or even editing configuration files.

I haven't messed with mods for a long time - my backlog is so huge nowadays that I barely have time to play the main games... But for some games like the Bethesda ones (FallOut, Elder Scrolls), it's way more fun to play with mods than even playing the main game. I remember playing with a lot of mods in Skyrim, Half-Life 2 and Max Payne; those were my most modded games. Some really good modders create entirely new games out of these mods, and these games may be really special (I particularly remember the Minerva mod for HL2 and Katana mod for the first Max Payne). You should remember that even Counter Strike started as a mod.

So, it's worth trying them, at least after you're done with the main game. The process is different for each game, but never too hard: just googling "install mods game X" is enough to learn about it.