Monotonous
You are playing a table top RPG and the GM is doing a great job. You are increasing in levels and then after awhile you start to notice that everything seems to be Monotonous. At what point does it become Monotonous for you? When you have passed the 20th level? When you become deity? When you see no end to a dungeon? Share your views.
Where campaigns begin to falter is when they finish the main aims yet decided to continue I.e. save the kingdom from the evil horde and players being attached to their characters want to keep them going with further adventures. From personal experience I was among these. However your characters get passed their prime in a sense, they have had their glory and future adventures seem never to be as good. Though I have had a few very good extended campaigns which did retain full character rpgs tend whole to be like movies, the sequels are never as good.
Playing God's is nearly always a mistake. Things that are often easy to explain become difficult to digest, what excuse would you use to explain a whole group of them hanging questing together? More importantly you need to imply vast limitations to Godly power otherwise the chars will literally be able to get away with everything, all attempts in this light tend to be inadequate. Faith is also a major problem, a lot of gods have followers how do these fit into a game? In my opinion its best to stay clear from the whole God issue
Yes when you walk and all scurry from your feet it gets tiresome. A friend would collect peoples adventurers that grew weary some and he would use them as the bad guys in adventures. I had a bad habit of losing character sheets so often this was not an issue. Also if you are stuck with the same group all of the time it was bad new blood was a big criteria to breaking boredom.
The "level grind" monotony isn't present in games that don't have the rather blatant class/level structure, though in some ways this is transformed into a different kind of monotony, as in the case with Call of Cthulhu, which only rates characters by their skills - this allows you to develop your favorite skills, but otherwise leaves you feeling like some of your secondary skills will never get very high, to the point they're useful.
I personally think monotony in a game in general depends on the moods and level of interest of everyone playing, from GM to Players. Sometimes you should take a break, do "one-offs" either just for one session or maybe for a few weeks, to play something different, maybe a different system, different genre, different style - it can get frustrating and depressing to play 1920's occult investigators stumbling over the mutilated and half-eaten corpses of orphans for three months in a row - take a break and play Toon or Paranoia or even just a fantasy game instead, get out of your rut, and come back to the other game later.