Well at least I can play tower defence fine

You can have a look at the arcade section of my forum for free N900 friendly flash games -> http://croggesserver.se/Serverforum/arcade.php

The forum for a private wow server which exists since years and is not related with mobile phones at all but the advantage here is that you have no advertisement or other things which eat resources while you are playing. It are around 120 games totally and a few which I tested like "Desktop TD" or "Boob Bubbles" work fine on my N900. I will add more games on request, just make a topic in the forum section.

I noticed that it helps to enable "Mouse Mode" in the N900 for games like tower defence, you can enable it by clicking on the lower left part in your browser.

Edit: Even more complex games like "rocket man" work quite smooth if you set the details to "low"

I also hope that it is not against the forum rules here to add the links in my post.