This is not a review of Internet Explorer 5.5 - HTML with Style | 6
So let's look at what we've got here. IE5.5/Win has implemented some CSS features that were absent from previous versions. It also has introduced some new bugs (maybe no more than one; my testing was not exhaustive, but I did not find any other new bugs in IE5.5/Win).
Another point is that IE5.5/Win is not backward-compatible with IE5 or IE4. Pages that worked fine under those browsers may now be unusable. Yet another point, which is equally important, is that IE5.5/Win is incompatible with Internet Explorer 5 for the Macintosh. Unfortunately I was unable to verify this myself as I have no access to any Macintosh computers (in Greece, Macs are about as common as rain in July. I only know one person who actually owns one, and he's on holiday. So I'm out of luck), however I have read numerous accounts from other CSS experts of how the CSS engine in IE5/Mac and that in IE5.5/Win differ in many fundamental ways (I am really unable to comment on the widespread opinion that IE5/Mac has an excellent CSS implementation as I have yet to see it in action).
The only truly meaningful conclusion I can draw here is that IE5.5/Win is yet another CSS implementation that is fundamentally incompatible with the CSS2 specification. In other words, if you create a style sheet as per the spec, it will do unexpected things when viewed in IE5.5/Win. These unexpected things will also be different from the unexpected things that are done by other browsers you are already familiar with.
So IE5.5/Win is not CSS2-compliant by any stretch of the imagination (not a big surprise). It is also not significantly more compliant that IE5 (not a surprise, but definitely a disappointment). It is also not close to the level of compliance of the Gecko engine. It is also in many ways incompatible with other versions of Internet Explorer in wide use today (this is a surprise, and a huge disappointment).