I think leashing can be fun but being able to do it so early (at harmony lvl 2 or something), and so often (at the cost of health), make it too, i dunno, not optimal. Plus, aliens get weak super fast, at the second level of unit upgrades, only worms and krakens matter. I think leashing should definitely come back, but either as a high lvl harmony ability, or make it cost expedition modules instead of explorer health. Or the Xeno Swarm, could be made into a specialized leashing unit maybe.
Some mods i usually use make alien life more relevant by giving them a strengh boost (i think they get +10% every 20 turns or so). It's a fun mod, and make aliens relevant longer. The best alien mod is one that wasn't converted for RT, which add several new variety of aliens, like a black worm that is weaker but moves two hexes; there was a weak manticore with range 3 i think, really annoying but cool.
Another thing that i noticed, is that at lvl 3 harmony or so, we get that "faster relationship recovery toward alien life" ability, but it makes the player go beyond neutral, once i hit harmony 3, it doesn't take that many turns to become allied with the aliens. The ability to befriend aliens should be there, but i don't think it should be achievable so easily.
Other notes:
I like the new artifact effects, but some are very weak (+1 vision for tanks isn't so good, +1 move i'd take). The buildings for the OERelics aren't that good as well, +2 production, +2 diplo. Maybe they could give an specialist slot as well, like a engineer slot from drone command, or even custom specialist slots: like a +4 diplo capital specialist from the frontier stadium. But i feel those buildings should be cheap since spending relics to get them is already a big investment, and with lower yields, everything takes longer to build already.
On 3 games that i played, i got at best 2 OErelic buildings, and i had to try really hard, so i felt that the trait "+1 yield from relic buildings" was kinda weak.
The +1 food to farms trait is really really good, i almost go for it every game. On my kozlov game, however, i had 8 or so sources of geothermal nearby, so i got the "+2 energy from geo" trait, and it was very useful. But unless i get a weird concentration of resources like that, the +farms is nearly always better. Don't nerf that, though! The generator trait could give +2 instead of +1, the mine trait could take care of the unhealthy instead, there are plenty of interesting options.
What else... would it be possible, eventually, to mod in hybrid version of planes and submarines, even if they don't get custom art? That could sorta take care of that annoying situation of having cool flying carriers with lame lvl 2 planes that die on the attack.
Also on units, i think all affinity unique units (all of them) could get a movement bonus. I have to go waaay out of my way to make use of the affinity units (hybrids included) when floating artillery and floating tanks are so much cheaper, faster, and take care of everything. Rocktopus, Sabr, and those hybrid dudes are so expensive in production, resources, tech, and they always reach the front when the bulk of the IA army was already taken care of by tanks, it's like a missed opportunity. I'm happy with their strength, i just wish they could keep up with the much cheaper and faster vanilla units.
Is there a way to tell the player a numeric value of our relationship with each AI, and how much we need for them to get them to sign diplomatic deals? What i mean is that, after getting a cooperation agreement, i have to check every turn until my "friend" will FINALLY allow me to pay for one of his agreements.
