I like Gantt.io a lot!

There are a lot of customisation options. Thats good because I'm not too keen on these monochrome templates myself - it took me a while to create my own larger number of colour shades - it was a bit of some effort, but the good news here is: it's possible.

There are also some minor bugs. The biggest problem I see at the moment is the handling on small laptop screens. Especially when setting colours, you only see a fraction of the setting "dialog" in the left sidebar and the many necessary scrolls are actually extremely annoying.

I see the greatest potential in using the time section for the timeline more like a filter.
It is the case that some graphics are not only prepared for a one-off presentation, but are used to report regularly to a steering committee. This means that over time more and more tasks are added, others are completed and the timeline becomes longer and longer.
Then it would be good to be able to use the date filter in the timeline to easily define the time window that is displayed. Elements that do not fall within this time frame (especially tasks) should then be hidden.
This is currently not possible and there is even a bug here that changes the start times of all tasks when changing the start time in the timeline.

All in all, I think gantt.io is a well-thought-out product, because you are not only limited to the predefined styles, but can also define your own. I also find the UI and handling (except for the problem mentioned above) very elegant and easy to use.

For me, Gantt.io is a recommendation.
I would currently give it a good 🌮🌮🌮🌮. Some bug fixing and the timeline as a filter would raise it to a clear 5 tacos for me.