I think tabletop simulator gives a really true experience to the game, and is better than Vassal for sure.  But now that I've experienced a TI3-like that can be played in 30 minutes, to a few hours, it's really hard to go back.  Also playing against challenging AI opponents whenever I want is a huge plus. Not to mention having all of the rules enforced by the game

I would call it an "iteration" on TI3 more than anything. People who really like TI3 (and are not pretentious about it) would probably consider Rebellion to be TI3 with a more widespread appeal.  The leaders are more like strategy cards than command tokens in my opinion, except that you can have many of them.