3G terrestrial worlds are probably very rare. When you pack that much mass into a planet, it tends to attract a lot of hydrogen during accretion. It is difficult for a terrestrial world to be more than about 2 Earth masses, which would put it at around 1.3G if it's iron or perhaps lower than 1G if it's carbon. Our planet is big and dense. Aside from Jupiter, which is a degenerate matter planet, Earth has the second highest gravity of the planets in our solar system. The only one higher is Neptune at 1.14G, because it is a fairly dense ice giant. Jupiter is over 2.5G but that's because its mass is beyond a certain point such that more mass added will not significantly alter its volume but instead will just increase its density. Gas giants like these may easily have very high G forces at their cloud tops, but terrestrial planets are not likely to be degenerate giants and thus will tend toward much lower G values.
Lower-G worlds could definitely host much larger life forms than Earth can, but most life doesn't evolve to be as big as it can be. We humans are near the upper limit of being easily manageable on land at our gravity, anything bigger than a bear needs a body built mostly around supporting its own weight. On the other hand, animals as small as mice have been shown to have high intelligence and complex social structures. This is why I think most of the people we meet will be smaller than us.
Life could potentially work on a solvent other than water, but the options are limited because you need something with a wide array of substances it bonds with and interacts with. The solvent doesn't just dissolve the organic compounds, it must be the main driving force behind their interactions. Water does that by far the best, but ammonia is another possibility because it is abundant and a very strong solvent. Life using ammonia instead of water would probably be much more limited in its developmental pathways because there are far fewer organic compounds that will form in ammonia. Silicon-based life is probably possible as silicon forms pretty much any shape of molecule that carbon will. But silicon-based life would probably have a slower metabolism and growth rate because silicones do not interact as strongly as carbohydrates do. Silicon-based proteins would have less energy and would be less active. If we found life based on ammonia and silicon, to that life we would probably be like the creatures in Aliens--ridiculously strong, fast, and powerful and seemingly able to do impossible feats.
Life might be more likely to start up in subsurface water oceans than on land oceans, because the former is far more common and far more stable. On the flipside, that stability could stagnate evolution. Life on a stable world will probably just be microbes until its sun dies.
I have noticed a common way writers differentiate humans is by saying we are creative or charismatic, it would be interesting to instead find that, more true to our primate roots, we stand out mostly by being conquering and nonconformist. Perhaps most peoples are more creative or charismatic than we are.
I'll bet it's uncommon for people to stand upright. Most life on this planet has a strong preference for staying low and sprawling out. Our stance is a terrestrial adaptation to an arboreal creature, a way to preserve stamina to make up for a lack of speed. We have a highly effective yet rather odd and ironic hunting style: we chase prey slowly over a very long period of time until we wear it down by our sheer ability to rest and regenerate less often and faster.
