I have used Open Office for the bulk of my work on Linux, OS X, and Windows for the last 5 years. With very few exceptions it works as well or better than MS Office and is compatible with MS Office files. The only issues I seem to have are almost always with legal documents.

If you need a Microsoft Office compatible tool, then OpenOffice is the best option. It's pretty good. If you don't need a Microsoft compatible tool, then you might want to try a different tool like gedit or Gnumeric.

OpenOffice.org - for all of its UI issues - is generally the default choice for open source Microsoft Office alternatives. It's not perfect, but it's the most feature competitive of the alternatives, and given that its UI is heavily Office inspired, it will be at least somewhat familiar.

Alternately, customers can choose from a wide array of options, from Lotus Symphony - which is not open source, but built on the OO.o codebase - to KOffice, a Qt based Office alternative with Windows and Mac compatibility.

Don't forget google docs, for simple document creation!

Given OpenOffice.org is the most comprehensive and widely used "good alternative to Microsoft Office", writing it off with a short provocative comment about UI isn't going to help much.

There are quite a few alternatives for each component (GNUmeric for spreadsheets, Abiword for word processing, KOffice, and plenty more) but all of them have a much smaller user-base as well as other limitations (such as not being cross-platform). To make decent recommendations, you'll need to explain exactly what aspects of OpenOffice.org upset you so much. We'll then likely be able to suggest alternatives that address those issues.

Having introduced many MS Office users to OpenOffice.org, I would firmly respond that the best free-software office suite that is “like MS Office” is OpenOffice.org (minimum version 3, preferably version 3.1 or later).

Just about every major function of an office suite is not only provided, it's provided in a manner easily discoverable by people experienced with MS Office; the terminology and interface style lead such users to find things where they are already looking for them.

Plus it comes with OpenOffice.org Base, whereas (AIUI) MS Office typically doesn't come with Access; and it comes with OpenOffice.org Draw, which (AFAIK) has no comparable MS Office equivalent, and is fast becoming a killer feature over MS Office for some of the people I've shown it to :-)

There simply isn't a comparable free-software office suite that meets your stated criteria other than OpenOffice.org.