"I put the Laughter in Slaughter."

• Pirates! and the bounty system
• The Skyboxes! (my favorite was the light blue one  - which sadly wasn't even carried over to rebellion as I remember)
• The voice acting! (Like Hoshiko's kinda stoned spoken: "Behooold my creation!; Ahhh... geeeniuss")
• The overall complexity
• The leveling of the capital ships

One of the things I feel Sins did extremely well is its streamlined macromanagement. A lot of RTS games require an incredible amount of attention and management in their economic systems, often disproportionate to the amount of strategy going on there. A game like Starcraft 2 requires incredible amount of attention to be paid to workers to keep them tasked correctly while also keeping them safe from harassment. Supreme Commander requires incredible focus to keep mass, energy, and build capacity in balance and games are often won and lost by who can run the most efficient economy. Sins of a Solar Empire, on the other hand, has a lot of the same economic depth but with much less management. Growing your economy is just a few button clicks, letting you get back to handling the fleets. If you're harassed, your focus is on getting military units into position to drive off the attackers, not scrambling the workers to keep them alive. The economic mechanics of Sins put the emphasis squarely on your military and commanding them.

And Sins still has plenty of economic decision-making. Budgeting resources for colonization and balancing tech expenditure with military growth were big decision points that had a lot of strategic weight behind them. It just didn't require much in the way of actual management to enact your plans, so your focus could stay on your fleet and the action.

The love to details was amazing. Voice lines and acting as people mentioned was superb, the little upgrades like demolition bots, lingering presence, probes etc. that enabled distinct play styles. The ultimate of the advent planet bomber cap aka the "shoe" was actually sinister and cool. Economy was great, if someone over focussed on trade (at least later on) one could leach from it with smuggling, resource focus etc. (or details like the Vasari being able to capture deep space neutrals with their scouts gave a great asymmetrical advantage to their early economy).

Artifacts and planetary bonuses always added some nice twist, even if one would pull a bad one with corruption or other debuffs.

Subtle storytelling was also something I was always fond of, so was the design and artwork of the original.

I loved the Hard Sci - fi artwork on things such as the research screen, I also loved the ship designs especially the TEC which do appear to have been cartoonised a bit for the sequel. Not everyone wants to play multiplayer all the time. 

I think this is a great and accurate perspective.

I hope that this philosophy is continued in the sequel, in particular with respect to micromanagement as it applies to fleet and combat management.

One gameplay factor I thought contributed to the success of MOBAs is that they automated a lot of the other elements of gameplay interaction that RTS games included, without eliminating them from the game completely. E.g. production was set to send units into the meat grinder, so the player had one job and one job only, and that was to focus their attention on one unit.

As an aside, every time I tried to play MOBAs I just got the overwhelming urge to play Sins of a Solar Empire.