Here's wot I think about default races and races design overall.
I've been looking only at initial stats, because techs give such a boost that the original race is somewhat irrelevant.
The data I used:
Ok, Lezgoon clearly suck. Tantik have 183-100=83 points left actually, due to repulsive, so they're fine, except diplomacy.
Kamzak (workforce!), Humans (early upgrade in critical areas) and Barbeck (colonize everything) are easy mode.
Everyone else is medium.
Noone uses barren, metallic or arctic planets.
Also, Gargal and Tantik can expand without bumping heads with anyone (except Barbeck).
Government modes do not work at all.
No changes whatsoever - no changes in maintenance, no changes in income, research, industry…
Fanatical ability works as another x1,25 on morale, may be useful.
Transient ability is a cheat as it allows far, far more faster exploration.
Immaterial and quasi-immortal seem the same. Also, they're an awful cheat, as they give 100% workforce and no need for farming - voila, 110k of research on the first turn (with Barsigs and good research).
Research points are calculated as (population_in_billions*workforce*scientists*10000 + 5000)*science_building_tier.
Good/poor research is applied by multiplying the result on 1,25/0,75.
So, buying level two on a fresh colony will give you more than level one on a homeplanet.
No race has unique and useful starting technologies, except for Barbecks.
Barsigs for some reason have 600+k food produced with only 400+k consumed.
Farming workforce could be shrinked to 60%, therefore boosting both industry and science three times.
Initial maintenance seems tied to population (I'm too lazy to calculate intercept on initial buildings, but I'm pretty sure it's linear).
Overall races are indeed quite different, but their differences do not stimulate different gameplay.
Some races are just easier and that's all.