I personally prefer it like they've made it. The only thing I'd really want is some sort of talent tree,so you can increase some of your current skills and perhaps give you a new one, making each and every character a little more "unique". Like some other probably have mentioned, with more classes there will be balancing issues. If they manage to balance the current ones the game will get far.
About content, it's still in beta. Take a glimpse of the game and I'm sure you understand how much work they've put down on graphics and performance etc, with that I mean, they ain't gonna let such a promising game go to waste
, they will probably put down a huge amount of time and work into making more/improving the current content once the basics of the game is working properly.
What I worry about is that fortress siege'ing will become tiring fast, and they've already stated that. But what can you really do to make it less repetitive? I guess different boss abilities but it doesn't seem that the AI of the mobs/bosses are that great yet. It seems to be "easy" if you follow the tank-and-spank method and make sure that people pick up adds fast/focus dps.