I will never understand why so many gamers are so impressed by D&D 3.5 rules.
Every RPG developer should make rules that work best for his game.
If every game would use the same ruleset gaming would get boring and each new game were just a mod.
I think one thing that's important is that 3.5 was open licence. Any other D&D rules system would have to be licenced. It was also the first D&D system to really incorporate non-combat skills well. Also it has a level of complexity and customization that later editions do not. Lastly there is a large degree of familiarity with the rule set among crpg fans.