I personally think that one of the major flaw of this game is that you can not level without being playing with other players. Some people don't think this is a problem because that when you play, there are a lot of other players that are playing as well. But some people live in a different time zone. Where as when they play, most other players probably went to bed already.

I think it would be a good idea to have some challenging missions that actually require time(say like 10~15mins each) and skills. And you get a good amount of experience and money depending on your level.