Good question. Remember that the first Z was recorded with literally no budget or production. It was Devin with a drum machine and his own recording studio. The final project was amazing, as usual, even more so given how limited his resources and attitude were. Not saying he didn't try, but obviously it's not as polished as his other stuff.
Z2 is much more histrionic. The presentation is huge. Some people are complaining because in a lot of the songs, the flow is "interrupted" by spoken dialogue. It doesn't really bother me. Plus, the expanded edition features Dark Matters without the dialogue so it shouldn't be a big deal. The album is growing on me because as usual, it takes a long time to digest. It's a great achievement. Heavier, somehow maybe not as melodic as the first Z, but great. The second song, From Sleep Awake, is simply wonderful. It's almost like a second intro to the album, after the opener Z2. Only 3 mins long with lots of subtle, simplistic but absolutely epic melodies going on. Dev gives awesome background vocals, too. Gives me chills when I listen to it.
Sky blue is great. Sounds like it picks up where Epicloud left off. The songs are a bit longer and Anneka seems to play a lesser role this time around though she's still very present. Again, look forward to strong but simplistic melodies. Not as many layers as his other stuff but still great music.
The highlight/surprise of both albums is the drumming on Z2. Ryan really shows his stuff and puts on an amazing performance.