Well I dunno what the issue is then because I get 20 hours at least out of every character I play.
I probably should've said "much, MUCH more than 20 hours."
Have you looked at my sig? Those are a few of my characters (I have a couple dozen total, and more all the time). They're dear to me. They're rich, complex, unique, distinctive, well-defined individuals. I've probably got a minimum of 40 or 50 hours into each of them, and I know that Kyla, Claudia and Bogmok are all well over 100 hours. And just earlier today, after not traveling with her at all for probably close to a year, I broke Kyla out again, to finish up the FG quest she was in the middle of and maybe to tackle the main quest. She's level 18 at the moment.
Never felt that the game got boring when I became good at something..
I do.
...if that is the case then just up the difficulty?
Because upping the difficulty just makes it more tedious. I don't want to make it take longer for my level 20 warrior in full Daedric to kill things. I want to take longer to get to level 20 and full Daedric.
Even so, there are so many other skills you can work on if you have maxed another one.
Sure, but why would Kyla - who grew up on the streets in Cheydinhal, learned how to fight and wanted more than anything else to go fight in the Arena, who then found that the Arena wasn't fulfilling and left to wander the land, putting her weapon skills to use to help people, and finally rediscovered her family heritage of nobility - decide that what she really wants to do is brew potions, wear a robe and cast spells? That's just not her personality.
Or create a new character?
Or a couple of dozen of them.
I guess people play for different reasons.. I guess the more important question would be whether or not you are a combat type of person or something else or a combination of the two.
I'm a person who loves to create interesting characters. It doesn't matter that much what sort of characters they are, so long as they're internally consistent and interesting. I've got a Nord warrior in heavy armor with a war hammer (that he talks to) who can't cast a spell at all. I've got a Breton Archmage who's never swung a weapon in his life. I've got an Imperial assassin who refuses to do anything that resembles work, so he relies entirely on illusion and conjuration. I've got a bubbleheaded female Bosmer who wears light armor and fights with a battle axe - she goes from airhead to psycho killer and back again without even blinking. I've got an Orc mage who's perpetually depressed because he thinks all the mages dislike him because he's an Orc and all the Orcs dislike him because he's a mage (actually, most people dislike him just because he's perpetually depressed). I've got a Redguard swordsman who refuses to wear armor, believing that if he gets hit at all, that means he's failed. I've got a Dunmer vampire assassin - a freelance Orc adventurer - an Argonian who fights with a selection of specialized enchanted daggers - an Altmer heavy armor tank - an antisocial Bosmer hunter - a naive and flighty Redguard waif - a Dunmer unarmored hand-to-hander - a Nord goddess/battlemage - an Imperial fighter in the middle of a mid-life crisis who just put away her Imperial Dragon armor, put on a slinky body suit and joined the Dark Brotherhood.... and that's still not all of them.
What do you consider to be fun in TES?
That's easy. Creating unique characters and getting to know them through the course of many hours and many adventures.
Each one of those characters that I weighed this post down with started out as nothing more than a bare outline. Bogmok, the Orc mage, was an Orc mage. That's it. I thought it would be interesting to play an Orc mage, so I did. Mindi, the Bosmer with the battle axe, started out as a female Bosmer with a battleaxe. Again, that was it - just that bare outline. All the rest - all the details of her personality that make her a recognizable and distinct character, came over the course of traveling with her. That's what I do with characters, and in order to do that, I need to be able to travel with them as long as possible. If the game just rushes along and next thing I know they're uber, then I never get the chance to get to know them.
There are plenty of games in which I can just jump into the shoes of a generic character and run around and kill stuff. There are damned few games - none that really compare to TES - that allow me to create pretty much any character I might imagine and watch them and learn about them as they travel through the world. That's the thing I most value about TES games, and that's the part of TES games that I'm afraid Skyrim is leaving behind.