You can hardly dispute that it is a good product, it has become the de facto standard for that reason - there are plenty of competitor products that have been around over time before the big Office boom.
The last time I used OO I found it fiddly, temperamental and unrewarding quite frankly. Simple tasks such as setting up margins were made awkward and didnt quite work as expected.
There are two issues. One is it any better than the latest version of other software available? Quite frankly it isnt providing you know what you are trying to do. In order to attempt to be more friendly there has been a load of excess dross thrown in and some items like the paperclip. You really like Clippy, do you?
Second is that once they were put into the position of supplying the base operating system and the software then there was no other possibility, they had to become the defacto standard for office software. Only a complete and utter incompetent in charge could have resulted in anything less.
To be honest many of the other packages available were less easy to use but the rampant use of proprietary formats made it unlikely that they would survive. Some of the opposition was better than M$ but people were blinded by the compatibility issue to any such factors.
Earlier versions of M$ Office showed that they were equally bad, it wasnt until the enormous monetary advantage was pushed into usability that it improved much.
Is OO actually any less over-killy? In my experience of using it, admittedly at least a couple of versions ago, it was pretty clunky really.
About the same, they are both chasing the same markets. To be honest there isnt a wordprocessor that just does the basics you need any more.