I have several years of roleplaying under my belt. Though I have only used roll20 for a couple of campaigns and those were DnD based, I have some experience with several other rules bases.
Included in (but not limited to) that is Dresden Files, Savage Worlds (and several subsets of it), Call of Cthulhu, D20 Modern, and just about every rendition of DnD from basic through 4th (have not tried DnD Next yet but would not be opposed to it).
I have found good things and criticisms to say about each form .