I was excited about ILUNA specifically for Aia, her design hits every note for me. As in, it's by far my favourite vtuber design out of everything I've come across in the last three years. Weeks after the debut, there's really no one I care to watch in the wave.
Other people in the thread have detailed her shortcomings quite well. In short, when she's not being actively off-putting, she's just dull. Half her jokes she misses, the other half she oversells. Her voice is good and I like the motormouth delivery, but she doesn't really have many interesting, relatable things to say. She's just being her character without really knowing how to make the character click.
That said, I'm not sure ILUNA is actually the failed wave they're being touted as. Catalog wants them dead in a ditch for not averaging HoloEN numbers (or just for being Niji in the first place), but NijiEN was never going to sustain CCVs like that anyway. Fans filter into the vtubing fan ecosystem through Hololive, everyone else exists downstream of them. There's no actual grounds for even competition there. The ILUNA debut numbers were completely abnormal, likely curious holofan tourists with nothing else to watch at the time. That Aia's holding 1k means she's pulling her own weight, at least, and the others are faring better.
She has plenty of time to improve her act, and I do hope she does. Meanwhile, the rest of NijiEN haven't gone anywhere, so I'll just go back to watching Enna and Elira.