I'm mixed on cytoid as well.
The lack of grouped notes irritates me, cause I have been playing on grouped mode in cytus 2 for forever.
Also, lots of charts are either terribly made or hard for the sake of being hard, rather than being an extension of the song. Dropped inputs and random fails really stand out in these "throw shit at the wall" level 15+ charts.
To continue wailing on it, the arcade timing really bugs me considering it's so hard to get a 100% perfect calibration. I can regularly clear level 15's in both cytus and cytoid, but I have been agonizing over 100% tp in a certain level 7 on cytoid for a few weeks now.
Overall, if you can find good charts it is a moderately acceptable open-source alternative to the cytus gameplay. There's a rating system in the chart browser that can clue you into particularly poorly made ones. I'm also fond of the character system released in 2.0, as well as the tiers system for certifying your skills. I hope in the future they can find better songs and associated charts to take advantage of these ideas.