Rimworld is a one of a kind game in my mind, so let's dive right in.

Firstly, let's get the negatives out of the way, and the only thing I have to say about it that is kind of bad would be the lack of vanilla content and the repetitiveness of the base game.

But that leads us right into our positives:
1A) Mods... glorious mods. This game has thousands of mods and plenty of them add hours to a play-through.
1B) The mods also make it less repetitive and allow you to do dozens of play-throughs without getting bored.
2A) There is an always changing sense of gameplay and your base will 95% of the time never be the same.
2B) Raids are forever changing and none of them are the same as the last.
EX: In my current run all my people have guns, half of which were taken off of dead raiders, and I got assaulted by about 30-40 people (due to dire raids) with swords and shields (due to a faction mod I have). They blitzed through my defenses and we ended up having to use my ever so precious rocket launcher (from Rimmunation), to blow them bits up.
3A) This is the best colony builder that I have found and definitely the most fun to play. Whether you want to let your people do their thing, or constantly pause and resume to get the most efficient, micro managed run possible, Rimworld allows you to do it.

I hope that you find this review helpful and maybe it even convinced you to get Rimworld. If it did, I hope to see your people on the Rim, whether they are friend or foe.