I think Tex is wonderful just as it is. It does have a learning curve, like any powerful system, but so does e.g. html+css or any programming language. Emacs is a great editor and I run it with a simple inotify script to get automatic compilation. The error messages could be better, but that too comes with experience; I can almost always tell exacty what is wrong from the error message. Tex is so well suited to the purpose of producing mathematical documents that I really think asking for a modern replacement is like asking for a modern replacement for HTML. If you are not interested in becoming an expert user, go with a front end (the equivalent of frontpage or dreamweaver or similar). For the heaviest users, learning Latex is not a big deal relative to the other arcane knowledge one must acquire to write something worthwhile with it. As others have said, the investment is paid off in beauty, speed, and control.