I just finished a game of Sins in the demo, and there were quite a few things that made me feel like I was playing a game I already owned, namely Starcraft.  There were just so many similarities between the two that I noticed.

First, both are played in real time.  Units, upgrades, and reseach topics all require a certain amount of resources and time to prepare in both games, and while the player improves his or her empire, others are busy doing the same.  This isn't a very meaningful point on its own, I admit, but it's still important.

Second, both games have the same type of units.  Frigates have short or long range attacks, and so do marines and firebats; zerglings and hydralisks; and zealots and dragoons.  There are siege frigates which specialize in planet busting and (if I remember right, destroying structures).  The similar tasks are done with siege tanks, firebats, and guardians.  There's a scout frigate class, and in Starcraft there are vultures, satellite detection, observers, brood queens (especially with parasite) and (arguably) overlords.  Capital ships are critical and gain experience points in battle which improve their abilities and gives them new ones, just like avatars in Warcraft 3.  There are also construction frigates which stay with their buildings like peons in Warcraft 3 and SCVs in Starcraft.

Research and upgrades funtion the same way in all three games.  Build a certain structure, spend resources, and in a couple minutes it will be finished.  Sometimes upgrades and research topics will require something else like an upgraded command center, hive, nexus, or planet, and they all do similar things.  Some topics improve attack or defense for certain units, others unlock new units or structures, and still others make it easier to operate efficiently.

Combat involves outproducing the enemies.  Zerg rushes are not impossible in Sins, and I was able to deal a telling blow against an enemy faction straight away with the starting fleet after a couple jumps.  Micromanagement exists in Sins wherein one pulls out individual frigates when they are damaged while the others fire on the enemies.  In all three games unit placement is important before commencing an assault, so the short range attack units lead while the long range attack units follow and the avatar or capital ship is surrounded or hangs in the rear (unless it specializes in close combat like the death knight or paladin).  Effective turret placement doesn't need a rocket scientist, and like in Starcraft, a good defense involves saturating the enemy attackers with turret fire.  Sins just makes unit placement and task force organization a lot easier, but I don't see any innovation in combat.

Now this is just based on one game I played in the demo, but the demo didn't convince me that it was a fresh gaming experience worth spending my gas money on.  I just don't see anything unique about the game except for colonization and jumping.