Alright, I have played through some missions on easy level (because I am such a noob), and overall I really enjoyed them. Some comments on them: (spoiler ahead)
Allied:
1. Red Dawn Rising: the first half is just perfect and reminds me of the RA2 opening. I struggled a bit since I was not familiar with units. (I also feel that defense structures are weaker than in RA2?). The second half is quite tedious attacking the Soviet base. Overall, this is an amazing one.
2. Eagle Fly Free: it's quite tricky on the first half. It's my first time learning that guardian GI can out-range sentry guns. After that, it is straightforward.
3. Road Tripping: a straightforward mission. I really like using the Stormchild.
4. Heaven and Hell: more like just hell, until I realized I needed to use a lot of auto-heal to deal with Tsivils. It's tedious using hit and run again and again though.
5. Bad Apple: I was lucky finding the barrack before landing troops on the main continent. The timing part is fun, and I almost ran out of time. After that it is not difficult.
6. Beautiful Mind: The first part is a challenge because there is so little time to reach the beacon. The rest of the mission is also difficult as the AI throws a lot of things at my base, and I need to destroy Iron Curtain and the amplifier in limited time. I think this is the mission that introduces a lot of more challenge than the previous ones and I like it.
7. Hammer to Fall: the desolators... trial and errors for the win...
9. Zero Signal: I decided to rush my force onto the north side. Siegfried is amazing and I love that he can out-range tesla coil. After 7 tries, I have managed to reach the Soviet main base and destroyed most of its production buildings. It's really fun mission.
11. Panic Cycle: I LOVE this mission. (ok well I just really like using Siegfried) AI just throw so many things to kill the MCV and the Battle Fortress. Even after establishing the base, AI won't stop (damn the Nuwa Cannons). It's reasonably challenging for the 11th mission.
12. Sunlight: the best mission of the Allied. Epic naval battles with a lot of resource. Killing all the Kirovs is always satisfying.
For allied missions, the difficulty for Easy is perfect, and they have a lot of variety.
Soviet:
1. Bleed Red: a good introduction mission. Capturing the Allied barrack makes it more flexible how to finish the mission.
3. Happy Birthday: after having Morales killed by dogs so many times, I've decided to not moving him until I clear out allied forces and buildings surrounding the Alamo and until I use spy planes to reveal the path Morales would take. A fun mission to play nonetheless.
7. Idle Gossips and 8. Death From Above are excellent.
11. Unshakable: this is it. This is the most frustrating missions because there are so many things going on and some many things that can fail. It took me 10+ times to finally finish it. It took me 5+ times to reach the construction yard. My problems were that I lost so many troops during the first Chinese wave before reaching the con yard, and that Morales' specialty in killing my own troops (and if I sent him in front of my force, terror drones always killed him). Even when I capture the con yard, it's very difficult defend my base and the seismic stabilizer, especially when the HUGE Chinese troops arrive. Finally, I used more and more micro-managing my force very carefully so that I have more troops when I finally reached the con yard. With more troops, Morales, all the Wolfhounds, and later Norio alive, defending my base is much less difficult. I love the challenge, it is fun, and it made me very happy when I was finally able to finish it.
12. Dragonstorm: another epic missions. A lot of enemies to kill.
Soviet missions are more difficult than those of Allied. I personally enjoy base-building missions.
I have not tried Epsilon missions yet. But so far, I really enjoyed most of the missions. Thank you, all people who are working on this wonderful mod!