The good thing about the Otterbox is that it makes the phone feel more solid and it does offer good protection from drops. The case doesn't scratch easily and even the dents from really hard falls are not that obvious.
The back cover is not difficult to remove. That's also what I thought until I read that you just have to start at the top of the case. Doing it that way, the back cover just slips right off.
The things that I do not like about it are:
1. Takes precious space above the keyboard making it difficult to type, but you'll adapt to that one.
2. Front cover hurts the ear when used in certain positions.
3. Difficulty in accessing the lock slider.
4. Difficulty in plugging large headphone jacks. I had to modify mine because of this.

I have one but it's not for sale.
(I'd buy another new N900 if I saw one sold at the same price you bought yours... that's a steal!!!)