I've you're looking to build something custom from primitives and you need ie support I would definitely recommend Raphael.js [http://raphaeljs.com/] They claim ie6+ support and in my own experience this has been true. Granted I was just making little dynamic pie charts, but they looked fantastic in IE6 (I'm actually surprised it isn't in more common usage by designers to certain visual bugs in IE6).
Raphael.js is really just a nice way to handle svg, and so it lacks some of the niceties of d3 as far directly tying your visualization to the data. But it's still a great tool.
After just having spent a couple days wrestling with g.raphael.js, I would recommend against it. The documentation is vague and incomplete, the generated graphs are inconsistent (e.g., points placed outside of axes), simple bugs with fixes in pull requests have been sitting for months with no response...honestly it looks abandoned.
While I don't have 2nd problem, I'm also considering alternatives to d3.js because of the 1st one.
I've seen that some people tried combination of d3.js and Raphael in order to overcome this issue (for instance: http://stackoverflow.com/questions/9559365/raphael-and-d3-js...), but I haven't tried it myself yet. I would be very interested to hear any experiences regarding this particular combination (d3, raphael).
The bonus with D3 is that (2) is up to you. Seeing as it's constructing SVG, you just need to design a plot such that it looks unique. I have a feeling that the reason why D3 sites look similar is due to copy & paste coding (which is adequate for most people).