There have been some very successful games. Back in the day Strange New Worlds (SNW) was one of the biggest things, but had some inherant flaws - very systemy, some staffing pains, etc. ATS Trekmu came out around that time and is still around. Kind of like SNW, but without all the wackiness that SNW had.
ATS is still kicking, and active from what I can tell, has 20-30 chars logged in consistently.
Some games like Gamma One, and there were quite a few others focused heavily on military organization and completing jobs, etc. It was very much like a part time job in some aspects, great people, great games, but it had it's niche.