I recently went through and updated the online game The Well, because after many plays through of it, I found certain parts, especially the beginning, to become more tedious. Instead of slogging your way through normal encounters, I wanted to spice it up with a variety of special encounters and monster variables.
The first thing I did was to add random monster boosts. Now, sometimes a monster will be "fast", which means you can't run from it as normal, or "Giant", which means it has a boost to its strength or charisma. There are many more random boosts, which help to make each individual encounter more exciting. They appear more often the further through the game you are, and also there is a chance that some monsters will have two at once, adding the further random element of what combination of modifiers might appear.
The next thing I did was to add about five special encounters at the beginning of the game which show up randomly, and give a player the choice of options as to how to deal with them. Most of the results give gold, experience, or items, in order to speed up the game. A few give out special new powers that increase the general power of the character.
The last thing I did was to make a bunch of little changes to item powers and encounter results, to make everything more balanced.
Overall, these changes make the game less predictable, and help speed a player through to the second half of the game, reducing play time and increasing the flow of the experience.