Having a view games under my belt I have the following observations. Keep in mind, I play mainly multi-player with a couple of friends, on endless.

• The Riftborn are head and shoulders above the other races. They get +20% production, +5 extra production per pop, assured access to both titanium and hyperium, blocking their outposts seems to to help much. Their disadvantages seem rather lackluster at the moment. Creating new pop is quite easy because of their enormous production, and the fertile penalty is rather weak.
• The Sophons' ability  is stronger in a galaxy with a few opponents and weaker with more opponents, simply because the chances of someone having not researched a tech is smaller with more opponents
• The Luminaris are stronger with an easier difficulty, because buying colonies and outposts seem to scale faster at higher difficulty.
• If you have access to the luxery resources, system upgrades with +x production/science are extremely strong and will make or break your early game.
• Sometimes the game responsiveness slows to a crawl, this can happen even if the game is in sync. For example the result of a certain action can take about 20 second to apply, or ships seem to move at a crawl.
• Reavers seem to spawn out of nowhere. In ES1 pirates spawned at systems in the fog of war, it seems to us that now they can spawn everywhere. Multiple times we have seen for example that a pirate fleet of 2 was approaching, only to be a fleet of 4 when they finally arrived. In addition, reavers always act directly on turn start, leaving you unable to take actions which you might have been able to otherwise, like passing a system if both you and the reavers are en-route, creating/disbanding/merging fleets, etc.

That said, we have a lot of fun with the game already.