Overall, I was a bit disappointed. However, I think this is in large part because I misunderstood the content.
In general, Interstellar Operations is broken out into two parts. The better half, in my opinion, are the rule sets for strategic battles and faction conflict.
The (other) first half is primarily rules for niche technologies in use during the different era. The tech tables are the highlight, such as when IS rediscover SL weapons and put them into mass production. Perfect for 3039 to pre-clan campaigns. Otherwise, I don't have much use for niche rules for prototypes, retro etc. I also don't see how that fits into the theme of Interstellar Operations. I would have preferred to see this content in its own technical supplement and have kept the focus on the interstellar ops, especially since most of the rules for equipment require you to be mostly playing at the tactical level anyways!
What I was hoping for were more rules for building star systems, fleets and large unit creation, the supplying of armies, how many mechs and vehicles are pumped out by different factories, and more rules for generating large scale units for the different factions in the different eras. The Inner Sphere conflict rules are interesting, but sparse. The diplomacy and economy sections being only a couple paragraphs each. That seems lacking to me. Shouldn't the different political structures results in different rules for generating units? Conscription versus volunteers, mercenaries versus regulars, how many mechwarrior graduates are available each year, etc. Icing on the cake would have been some reconciliation of FASA economics when it comes to factories, transportation, ship construction, etc.
Overall, I give it a 3/5. The large battle rules are great, but I'd rather have seen less emphasis on equipment and more on coordinating battles across whole fronts and how to interweave factional politics and economies into the military mix. It looks like the potential release of Campaign Companion might have some of that.