Quick reply.
> what are some apps from app manager can you recommend?
Here are links to competitors of recent contest. Theoretically, they should be the best apps for N900 existing.
Games:
http://talk.maemo.org/showthread.php?t=58990
I personally recommend PeQersi.
Desktop:
http://talk.maemo.org/showthread.php?p=760304
Graphics&Multimedia
http://talk.maemo.org/showthread.php?p=763679
I have chosen Metre.
System & Utilities:
http://talk.maemo.org/showthread.php?p=764039
Location & Navigation:
http://talk.maemo.org/showthread.php?t=58964
I voted for ModRana. MetroMap might also be useful.
Other:
http://talk.maemo.org/showthread.php?t=59038
And one more link:
http://talk.maemo.org/showthread.php?t=59074

>first, how come when i adjust the brightness of the screen, let's say to 2/5, it still goes to 4-5 brightness? is this a problem or do i have to do some adjustments?

I haven't experienced this.



And, check what version of operating system you use. Apps->Settings->About product
Updating solves some problems.