For DLC and general improvements this is my feedback:
Right now the game has a major issue with replayability. There are several factors contributing to this:
1.) Once the main campaign is complete there is very little to do. There is no reason to explore, few side quests, a small number of easter eggs. Replayability of SC:O is very very low. After I finished the main campaign, I haven't booted the game back up. This is a serious issue because it took me little over 13 hours to complete the campaign. Although I'm a founder and an original SC2 fan, I can't see how an outside gamer can justify the cost of the game with the current package of content offered.
We are in a post Skyrim world where single player games are expected to be loaded with content, especially in a game with the universe as vast as SC:O. The reality is, the universe is really quite empty. In SC:2 there were many aliens to interact with (more than SC:O) and many of them were not integral to the main story.
In SC:O almost all aliens are required, there is no reason to explore outside of the confines of the main campaign to discover new aliens. Without immediate expansion, I don't think the game is survivable with its current content package.
2.) Lack of challenge. There are no superbosses, no challenge encounters, and nothing to really draw the attention of the player in terms of completion or difficulty after the campaign ends. Part of this is due to how laughably OP you can make the flagship. One of the major problems are deflectors. Deflectors are so stupid broken you can just load your ship with them and take 1 damage from the most powerful enemy attacks. This removes all elements of strategy from the game.
Deflectors and the type of hard damage removal they add without any penalty need to go. There are also some incredibly overpowered weapons (Earthling Fighter) that trivialize encounters. In the case of SC, no matter how powerful you made the Vindicator an UrQuan Dreadnought or a Kohr-Ah Marauder could still easily kill you. The Vindicator and the most powerful alliance ship, the Avatar, was also completely useless against the Sa-Matra, forcing you to use other ships to complete the game. This is a better structure of balance than what we have in SC:O where I pretty much fell asleep taking 1 damage from black hole missiles with my 4 deflectors and cheesing every enemy ship with the gatling laser.
Expansion of the game is 100% needed right now, there is not enough content to keep players happy. There are no endgame challenges, no reason for exploration. There are no alien races outside of the campaign ones. There are also some fundamental player challenge issues and systems that are downright broken and need to be fixed.
1.) Nerf the hell out of deflectors next update.
2.) When adding new campaign DLC add easter eggs. Add new alien races and side quests but DO NOT tell players about them. Don't even put them in the patch notes. Let players discover the universes' secrets on their own.
3.) Add some rings to various gas giants. It's silly that saturn is the only one with a ring.
4.) Add side quests and updates to existing alien races that give the player unique rewards with them (access to more powerful ship types, upgrades to ships of other races).
5.) Expand the Lexite story. As I suggested before, it may be good to allow the players to start a new arc of the main game from the perspective from the Lexites using a new flagship.
6.) Add some extremely hard alien ships in deeper and unknown areas of the universe. An example might be an evil Jeff probe called Bob that will just WTF own you without the right setup. The Harmony and Amorata were good but you can still trivialize encounters with them using deflectors. There also needs to be tangible rewards for meeting these challenges.
7.) Make player choice matter. The campaign was extremely linear. Your choices should have more consequences, leading to alien races leaving the alliance and becoming hostile, alien races being wiped out, or turning former enemies into friends. There should also be hard choices. Some races might hate each other and the player has to choose between being friends with one or the other. The Mukay and the Greegrox is an example, let the player have one but not both.
8.) Dyson spheres.
ALIEN RACE IDEAS:
1.) The Ouma and Varla. The Ouma is a race of moth-like creatures that are relatively peaceful and SoS the alliance for help. They are being attacked by another race of evil worms called the Voor. The Voor believes they will ascend to the next level of evolution by consuming all of the Ouma. The reality is that the Voor are larval forms of the Ouma that were genetically experimented on by the Scryve to become soldiers. They were deemed a failure but continued to multiply, consuming the Ouma to correct their genetic deficiencies. The player can destroy the spawning pools of the Voor to wipe them out, assist the Voor in consuming the Ouma to become genetically complete, or convince the two races to merge into one new race called the Varla that has powerful ships (best outcome but hardest to reach). You can see here where player choice matters.
2.) The Sygzy are an alien race that live within a massive dyson sphere. Their sphere is running out of power and they are travelling to a nearby star in order to consume it and remain operational. There is a race of fuzzball non-space faring creatures called the Polpik that will be destroyed if the Sygzy consume their star. The player can intervene by providing the Polpik with a colony ship so they can escape before the dyson sphere arrives. Alternatively they can destroy the dyson sphere. If the players evacuate the Polpik to a new system, the Sygzy will later provide technology to the Polpik that allows them to become space faring as reparation for destroying their homeworld. It is heavily implied that the creator of the Sygzy is Jeff.
3.) The player finds ruins of an alien race called the Memnon, the players follow a breadcrumb trail of empty temples left by them that indicate that the Memnon believed they have found a gateway into their version of heaven and "ascended" from this world. The players discover that the Memnon gate is actually another origin. The heaven that they believed they were ascending to was actually the stomach of a quasi-demensional being that is now consuming them. The players can assist the Memnon generation ships trapped inside the being and free them.