I really loved how you spent your legend points(xp) to level up. For those who haven't played it, even though there were classes and levels the levels didn't have the same impact as levels in d&d. Really leveling up gave nothing tangible to you except maybe one minor benefit. What it did is allow you to purchase the talents of your new level at the normal cost. You could purchase talents from almost any level at any level. A level one calvaryman, could purchase a cool talent from the 8th level class abilities of his class. You could level up, not from having the right amount of xp, but by getting a certain number of talents from your current level and lower to a certain rank, which also I though was a cool way to do it. I knew of some people who never leveled up much at all, they just blew wads of karma on one or two talents becoming experts in a narrow field, but never gaining the requisite experience in a wide enough area to level up again.
Also gaining another class was more difficult than 3rd editions yeah my next level is wizard, I know I haven't trained at all for it yet thing. But it was quick, and if you had enough karma to spend could be done in a very short amount of time. And if you didn't want to pick up another class, and weren't human, but you really wanted an ability from another class, you might be able to pick it up as a skill as opposed to a talent. Skills being nonmagically enhanced talents in many cases.
Add onto it that they ahd a lot of other cool rule mechanics and a great world and it is possibly my favorite fantasy game, and definetly more well liked by me than 3rd ed.