If you are interested on a D100 / BRP / Mythras traveller style campaign M-Space is a must have.
Even, if you are interested on other scifi flavors, M-Space is a god point to start.
It add to Mythras several interesting rules, circles, extended conflicts, simplified combat and a different approach to Psychic powers than Luther Arkwright or Classic Fantasy.
The circles are a kind of cult with several characteristics like influence or power that you can use for create societies and factions, for example you can use it for define the game terms from a Band to a interestellar megacorporation.
The extended conflicts are adapted from RevolutionD100, and are a very interesting tool that you can use for increase the drama, personally i believe that the consequences are to big and i personally prefer my own home rule that uses passions like 'aspects'.
Simplified combat comes from the extended conflicts and faster a lot the combats if your groups is more interested on other aspects of the game, personally, since the general rules comes from Mythras imperative i miss the inclusion of the rules showed at Mythras firearms, that are just the opposite.
When we arrive to Psychic powers we can see that the original game comes from BRP and they don follow the Mythras standard of 2 different skills. I dislike that a little but it is more a personal taste than a real problem. At the other side, there is a kind of powers tree, and i like to have requirements on the most powerful levels.
The specific scifi toolset comes with starships, alien creation and solar systems / planets rules.
Starships are created using modules, and are generally enough for represent anything you imagine except maybe, biologic ships or other exotic stuff.
Aliens and planets are far away from MindJammer but still they are quite useful.
As a negative aspects, the book format is squared, which it should not be a problem unless the big exterior margins they have , it feels like a waste of space. Also, i would preferred some more inner margin to facilitate reading. I miss some more weapons, vehicles and equipment examples but definitively M-Space expands smoothly Mythras towards SciFi.
There are also a very interesting settings, of which Odd space is my preferred one although i don finished the reading of the last ones (elevation) and my opinion of it comes only from external reviewers.
if i could, i would rate with a 4.5 aprox.
A must, as i said at the beginning.