Openmode is certainly useful, you will notice that without it there are still many barriers, even as root.

Regarding other browsers:
I personally think, most aren't worth it.
One notable exception is Opera, it can display many pages where the basic browser fails and is faster. But be careful, it drains your battery.

Make sure to get a current N9Qtweak and activate the patches for drive. Traffic view doesn't work any more, but other features come with it, like toggling between ETA, remaining way and remaining time (Tweak menu G).

The Low Power screen is always pixelated, thats part of the powersaving I guess. If you make it white its a bit sharper.

FBReader on the N9 is amazing, Even more so paired with calibre on your PC. The OLED screen makes reading so enjoyable and in flightmode you can go for more than a week and handle it like an e-reader. If you can resist playing with it that is.
You might enjoy my guide: http://talk.maemo.org/showthread.php?t=97131

Stellarium is also great, allowing you to view the night sky, you can take your phone and point it at the sky, seeing the constellations in front of you.

If you enjoy mobile games, the preloaded Galaxy on Fire is quite a good one, although you will be frustrated when you discover all the nice extensions for Android you can't have.

Fahrplan allows you to navigate public transport in many different countries and uses very few data.

MaeFlight is rather buggy but still good enough to help you get fast Flight information.

GPSMeeFo helps you if you are as impatient as I when waiting for a GPS fix. No, its not faster, but you can watch the progress.

Helium is great paired with Kodi to play content.

AGTL for Geocaching if you are into it, its slightly buggy but in general it works. Some caches crash the parser and your download fails, so don't attempt to download larger areas at once.

cutemeter for fast measurements of small objects

I remember Camera Pro as being useful, but my N9s camera stopped working.

Personal Web Server as quick way to view your IP and to share files with any device.

Those are all Important ones I use often.
Disclaimer: I use a N900 as main phone currently, but have the N9 as backup, eBook reader and stargazing support always with me.