I have really bean enjoying RPG Circus over the last few days. One of the coolest things they talked about, which I have always wanted to do myself (and hopefully will be doing in my current setting) is the creation of BIG CREATURES that are actually really, really big.
In season 1 Episode 3 of RPG Circus, they talk about drawing inspiration from things you see in the world. One of the examples they gave of this was creating monsters that mimic those of Shadow of the Colossus for D&D 4e. These creatures aren't something that can easily be slain, but rather, are something that the players can climb around, attack, and also try to bring down via a variety of skill challenges.
If you remember, I brought up the 12 Great Beasts of the World in one of my previous posts regarding my current homebrew campaign. I wanted to make these 12 Great Beasts modeled after the 12 Animals of the Zodiac, but also have them be totally twisted and extremely large in size. Bringinng one of these beasts might be an adventure all of its own. An extremely dangerous adventure, but one which could be extremely fun and world changing for the players.
I guess all I really have to say is that good stuff is good stuff. If you look at a game like Shadow of the Colossus, you really can't help but want to have something like that in your role playing game.