When I learned about the new Shadow Isle map, I was really excited. When I learned that it will replace Twisted Treeline, I was still excited, but disappointed at the same time. This thread addressed my concern exactly.
I feel the Twisted Treeline maps is fine as it is, even though I play a champion that's considered as a disadvantage on this map. I actually enjoy this map more than Summoner's Rift. I appreciate Riot addressing the turtling strategy in the new map, but I feel the turtling strategy is a real "strategy" that is totally reasonable and not a "bug". To take that away means you are forcing players to play this game one way. Not a really great way to broaden demographics.
People should be able to play Summoner's Rift, Twisted Treeline, Crystal Scar, and/or Shadow Isle at will. I prefer to play all four.