Major changes in 2.x charts version:
Unified data model. Now you can create only one data model and it could be used with wide ranges of chart series. For example, if you want to show the same data on bar and line charts, you can pass the same data model object to both charts without any changes.
Simplified charts architecture. There are no more SomeChartTypeChart class and chart's hierarchies. There are only Chart2D and Chart3D classes. All the chart types are now available as _Type{_}Series classes. Now the several different series could be easily added to the same chart. For example you can easily mix line series, bar series, and scatter series on the same chart, using the same or separate data for your series at your choice.
Simplified series. instead of using many variants of same series class, the unified strategies concept is used. For example, Instead of creating PercentageBarSeries, we are creating regular BarSeries and specifying available drawing strategy: Percentage. In this way you can change series representation on the fly, without reconstructing data models and series objects.
Unified styles. The charts visual appearance is no longer controlled by setters and getters on series, chart objects. All the visual settings are stored in style object. The style can be saved/loaded to/from file and reused for other charts, series.