RftG, in terms of gameplay, falls fairly in the middle of the two other games. Similar mechanics of role selection, cards as money, 'big building' cards, victory points, shipping strategy (consume) vs. building. There's slightly more relevance to role selection in RftG than in San Juan, but not as much as in Puerto Rico. Seating order doesn't matter as much as in Puerto Rico. In terms of learning, San Juan is easier to teach because it has a more accessible theme and RftG has an intimidating iconography.
Still, it's a game where it's hard to make real mistakes, just sub-optimal choices, so winning is usually determined by luck, game experience, and familiarity with the cards.
RftG has more luck than Puerto Rico, since it's based on card draws (even though this is mitigating by multiple reshuffles per game). Still, all these games are 'group solitaire games' at their core.
I'd only suggest RftG to someone with some 'real' board game experience (i.e. not Monopoly or Apples to Apples), AND if they enjoy the space theme. Rules take about 45 minutes to explain fully, but this can be done, in part during a first practice game. Strategy isn't as important in RftG as it is in Puerto Rico, as the extra randomness tends towards good tactics being more important. This is because it's a progressive build game where early decisions affect victory point 'velocity'. Strategy comes in when you know the cards and can selectively optimize for one or more 'big building' cards, and usually is only relevant fairly late game.