What's left after Ascension?

Well I ascended, and would now like to know how much is left in the game for my character. I read somewhere that most of the game content is for post-20 characters. Is that true?

Are all the best skills ahead of me, or behind me? How much further does the story go on?

I'd recommend you continue through the game and find out- you've still got a lot of missions to go for the storyline, not to mention a huge number of EA's, things like the Worlds at War areas, getting better armor/weapons, and of course, PvP. I've spent probably twice as much time in-game after ascending than I did reaching that point with my current character, and still haven't gotten anywhere near finishing the content- I haven't even been to a lot of areas, and there's tons of elites even for that one character that I haven't managed to capture yet(got ~10 of them so far)

Pretty much all of the Elite skills are only available after Ascention(there's a couple availabel before, but not many), and they're only obtainable via Signets of Capture.