Before saying anything else, I need to be up front about a couple of things. First of all, I'm not a Biblical scholar. I'm just a seminary graduate with an interest in these matters. Secondly, since the new NIV has only been publicly available since Monday (and that, only online), I've by no means had a chance to read through more than a tiny fraction of the whole text. I am depending heavily on the observations of others. The good news is that BibleGateway.com, after initially removing the links to the TNIV and the old NIV in favor of the new version, has restored those links, so you can compare versions quite easily. I recommend starting with this link, and working from there if you want to do you own informal comparisons.
My initial reactions are better than I'd feared. The new NIV is far closer to the TNIV than it is to the old NIV in many respects, including the area I've focused the most attention on: gender language. My concern, as I've tried to describe it in comments elsewhere on the web, has been less with "gender inclusive" language or "gender neutrality," and more with not being "gender exclusive." Many readers may feel that this is only a subtle distinction, and maybe they're right, but I am personally most concerned that would-be readers of the biblical text not feel excluded when the original intent wouldn't have warranted it.
This is certainly not to say that the new NIV is perfect (no translation ever is) or that they haven't ever backtracked where the TNIV was better. To use just one example that Joel Hoffman points out, the change from "people" to "man" in Matthew 12:35 (for ἄνθρωπος, which suggests humanity more than maleness) is a bit inconsistent with less gender-specific usage elsewhere in the new NIV. I assume this particular instance was done because there was concern about the shift (in the TNIV) to plural, which the translators' notes to the new NIV indicate that they tried to avoid when possible (this is different, by the way, than the use of "they" as a singular pronoun, which is becoming increasingly common in modern English), but why not use "person"? That said, by avoiding plurals where the original text was clearly intended to be singular, I do feel that the new NIV is more accurate than the TNIV was in at least that respect.
A quibble of mine is the use of the word "mankind" in the new version where the TNIV had used other words like "humanity." I'm not sure I understand the motivation in this case. My concern with "mankind" is less that it suggests "male-kind" and thus would potentially exclude people, and more that I don't feel that "mankind" is in particularly common use today (compared to words like "humanity").
Here's a quick list of sites that have given more observations about the new NIV. They seem to reflect a diversity of positions on the theological spectrum, and thus I hope that it represents a fair accounting of what's going on.
One final note. The division over the TNIV was so strong that many well-meaning Christians have figuratively thrown their hands in the air and asked "why all this fighting? These are debatable matters!" And, of course, there is a large extent to which they are right. However, I do think it's appropriate to acknowledge that there are good reasons why people are so passionate about these matters. I, for one, am unwilling to concede that gender-exclusive language (when sound scholarship tells us that the passage was understood inclusively in the original context) is an "equally viable choice." I thus intend to defend my position when it is attacked. However, I do hope that I can do so with a sense of perspective. People come to their positions (whatever they are) for a variety of reasons, and it is unfair to attribute malicious motives to most opponents. I hope that the debates that come in response to the new NIV, however passionate, remember that we are all God's children, and are conducted with a greater sense of respect than some of the debates of the recent past.