Imperial Settlers verdict: Good! We both like it after 2 plays. She even asked to play it again the same day which is always a good sign.
The first game I only won by 1-2 points, normal rules but we didn't bulldoze enemy properties. The second game, we played the "peaceful" variant even though we basically did it before. One big change is that with the actual peaceful variant rules, both players get a random common card each round. We were swimming in cards.
Race for the Galaxy with The Gathering Storm is still my favorite tableau builder (and one of my favorite games), so I thought I would make some comparisons.
Time to play
I think Imperial Settlers should be shorter. In practice, especially with the peaceful variant and more cards, we both had massive hands. Unlike Race for the Galaxy, there isn't a hand size limit so you can be digging through 12 cards trying to figure out the optimal thing to set up. Both games lend themselves to paralysis with all the interlocking choices and the desire to BUILD ALL THE THINGS.
Setup / Teardown / Fiddly Bits
Race is mostly cards besides a few goal tokens and a bunch of point chips you have to count up and hand out. Imperial Settlers has 7 types of little pieces you regularly throw around, but they're easy to tell apart. Other than that, setup and teardown are simple. The decks are even easier to maintain than Race since you don't have to pull out start worlds.
Single player mode
Both games (with The Gathering Storm) have singleplayer modes, which I appreciate. I haven't played either, but the Race for the Galaxy singleplayer looks way more complicated. I suspect Imperial Settlers does something simple to block/attack/challenge you.
Complexity
Imperial Settlers is simpler. All cards affect one of 3 categories, and all phases of each round always occur. In Race for the Galaxy, cards can affect multiple out of 6 possible phases, and not all phases always occur, and the details of the phase differ depending on whether you selected it.
Clarity
I'd say Imperial Settlers is clearer. A couple things aren't visually explicit (production/deals give you the bonus immediately, and deals require 1 food) but most things are simple. There are fewer and simpler symbols than Race's massive symbol overload. In addition, it can be time-consuming to scan your Race tableau to see if the current phase is affected. In Imperial Settlers, deal cards and production cards sit in their own row, so it's easy to see what to scan. General "feature" cards sit in another row so you can pick them out, and cards you can activate are in a third row. Faction and common cards are put in different sections and color-coded to pick out easily.
One negative, the faction decks tell you how many of each card there are (so you know if something is rare), but the common deck DOES NOT. I don't know why, since this can be pretty important (there is only 1 Monument card in the entire deck).
Interaction
Race for the Galaxy is basically multiplayer solitaire besides competing for goals and observing what cards the other player took from the deck. The phases you pick affect the other player too. Imperial Settlers has more interaction if you use the normal rules that let you bulldoze enemy common cards (or Japanese faction cards). There are also a few random cards that let you affect the enemy in some way. If you play with the peaceful variant, it's still possible to screw over the opponent with certain cards, but you can choose to ignore them. I suspect the balance is affected slightly.
Determinism
Both games depend on random card draws, but Imperial Settlers has a public draft phase each round. I'm not sure how useful the information is, but you can at least see what other players pick and potentially block other players from grabbing certain cards.
Symmetry
Players in Race for the Galaxy are identical besides a single random start world. Each player in Imperial Settlers has a unique deck, unique starting production values, and a unique resource / token type they can save between rounds.
Mechanics
You can use cards in Race for the Galaxy to build your tableau or to buy other cards. In Imperial Settlers, you can bulldoze cards for an instant bonus, make a deal to gain an instant bonus + production every round, or build them for their normal effect. There are also a ton of action cards that let you transform various goods into VPs / other goods. The draft mechanic plus the triple uses of most cards plus the variety of goods plus the assymetric empires is enough to make Imperial Settlers feel different from Race, in my opinion. You can use gold tokens as a wildcard for food/stone/wood resources, which is a neat idea. Another cool thing is that besides your one racial storage resource, you lose ALL YOUR RESOURCES between rounds, so it's spend it or lose it.
Balance
I suspect Race for the Galaxy + The Gathering Storm is more balanced. I haven't played as much Imperial Settlers, but it still feels fairly balanced. There are some potentially strong mechanics, like the card my opponent used to gain 1 extra VP every time they gain 2+ VPs, or Temple of Ra + Swimming Pool to take over enemy cards temporarily. As mentioned earlier, playing with the peaceful variant may also affect balance since some races are intended to be good at gaining/using bulldoze tokens or whatnot.
Presentation
Imperial Settlers has a nice cutesy fantasy atmosphere and cohesive visual design. Race for the Galaxy has nice art on the cards that is very scifi. Race's overall presentation is modern/minimal/technological.