It's very good - how can chartreuse drinks be bad? but there isn't much going on outside of that. I upped it to 15ml of each chartreuse and it's a vast improvement but the chartreuse is doing basically all of the heavy lifting of the 4.5/5.
Whilst the taste is overwhelmingly that of campari, I think the quality of the drink hinges on the limoncello. I used the dregs of a not-so-good one and it was fairly flat outside of the campari flavours. I imagine with a good limoncello this would be a good drink rather than a pretty okay one.