I have the base game, the first hero box and "Something Wicked" large box expansion. There are also two or three villains available to download from their website.
With all that stuff I think your amount of replayability is extremely high. The game can be played solo, collaboratively (alone or in teams), or competitively (again in teams or single players). If you have a small number of players I wouldn't recommend using any of the large board expansions, because the traveling distances become rather tiresome.
The cards and components are excellent. I've heard of people spilling coke on the cards, rinsing them off and not having any problems. The figures are very close to 28mm / 30mm scale and are very good looking. I haven't painted mine, but I've considered it more than once.
I really enjoy the game and it's one of the few that the gf will actually ask to play, so I consider that high marks.