I picked this game up one afternoon during the summer sale and started playing.
When I stopped, it was shortly before sunrise.
So it's rather successful by that measure. It's quite satisfying to take back ground from the creeper, and when one word is safe, jump right into the next. One more level. I don't think I've played the other Creeper World games, but it feels like after years of making them they've got a pretty good handle on what makes a Creeper World game work in that regard.
I've just finished the main Arc Eternal
campaign, after 27 hours. (I play defensively and pause a lot. Your mileage may vary.) The campaign is pretty good at making each level just a little different, providing some new element of challenge and giving you a new ability to use. Some levels are more different than others.
The game's weakest moments, I think, are the maps that become simply an ocean of creeper. Any distinctive features of the terrain are all but lost under the sea, as you slowly entrench and advance. Maybe more aggressive tactics could prevent ending up in that situation, but since I wasn't actually losing
those battles, I didn't give up and try different techniques. Then came along a different map that makes things interesting again.
This isn't the sort of game you play for the story. Yet there is a story, told in bits of dialog at the beginning and ending of levels, which shows some significant thought has gone into the lore of the Creeper. I might have appreciated it more if I was familiar with the other games, but it provides some interesting atmosphere.
I can't comment on the other content outside the main campaign, but there seems to be a lot of it, with a strong focus on giving the community powerful tools to make more.
I played this on Linux (Ubuntu 14.04). Everything ran great there; the only hitch I found is that after switching out of the window with Alt-Tab, I had to hit Alt again after returning to the game to get the keyboard input recognized correctly.
To sum up: Surely not everyone likes this style of game. But if you're interested in this sort of thing (which you likely are, if you're looking into the reviews), I recommend it without reservation. It's an excellent implementation of the idea.
And also very good if you want to forget to eat or sleep.