If you are looking for a challenge, you could give the fix mods a try:
MarvinKosh's Space Weapons Fix Mod
Tolmekians' TechTree Fix
Autumn Twilight by me
and Altarn's Polished Twilight.
Their main purpose is to fix the tech trees, allowing the AI to play better. There are also several balance changes, new techs, new improvements, and so on. Just take a look a the mod description and see if anything strikes your fancy.
As for different race abilities, I made some changes to them in my mod. Plus, I also added a few new options to customize your races' starting abilities, and tweaked the values of some of the existing options.
If that isn't enough, you could use my new mod Negative Abilities. As the name suggests, it adds options to make your race start out with negative ability scores.