For myself, it hasn't been so much about lack of challenge but, rather, more about lack of diversity.
I wish I could actually do the things the development guys keep referring to in their GW posts and other places concerning using multiple build strategies, etc. That is a fantastic idea! Too bad it simply is not possible in their current model.
You either are extreme P2P to get that diversity or you end up using the same 5-8 toons over and over for everything. If you are the P2P, you suffer from having the diversity but not enough other people with your diversity level so you keep fighting the same team setups far too frequently. PvE becomes your only change; however, the PvE game can never be at the hardcore P2P level as it would shut out too many players causing far to great a reduction in players (and, as such, more diversity loss).
So, I conclude the problem is with diversity and availability of it. If everyone had more access to a more diverse portfolio of meaningful toons for team building, the game would be far more robust in all game modes.
