Just to help out, on the matchmaking, it may be best to switch over to "Gold". Go to settings, then look at the bottom. Lets you play with the trial members, and anyone that has issues with the new patch.
I think with all of the upgrades you can get outside of the game, as well as the constant upgrades inside, it will have plenty of replayability.
Good guardians on personal experience: Agandaur, Lugbol, Gandalf, Galadriel, Ewoyn, Sauron, and Ugluk. The others I haven't got a good indication of the capabilities. As far as I can tell, provided you can get a good mix of roles, you can't go wrong.