Coursera is somewhat different from both edX and Udacity. Unlike Udacity, but like edX, it's a non-profit. edX has been building out its partners, but Coursera already has more courses and partner universities than the other two.
The course list does have a bias towards math/science/tech, I think, but they have a lot more non-math and non-science than does edX (Udacity, of course, has a heavy math/tech bias).
I tried a couple Coursera courses for a few weeks, but like with MITx/edX, I had to drop them. The problem I've had with the edX/Coursera setup is that there are still specified deadlines, and there's not a lot of wiggle room there. I understand why they'd want to do that, but for adult learners who are doing this for enrichment purposes, having courses starting on specific dates and progressing through them week-by-week really doesn't harness the power of the internet and the desire to have on-demand content.
Everybody is learning as they go in this new approach to online education, and I imagine they'll knock out the kinks. I seen that, perhaps in competing against Udacity, some courses have been made more "bite-sized" - running only 5 weeks as opposed to a more semester-like 15 weeks.
I see they've already improved their website in a year, and I see they're hiring more to help on the tech side as well as people to improve learning so I imagine Coursera will improve even more as time goes on.