I think spinoffs is a great way of showing the potential of a franchise without the need to stick to the usual game's rules and world.
PMD is a brilliant example on that. It sounds a bit silly at first, and looks it too. But PMD2 especially is a very deep game, not to mention the music was UBERSOMELY nice compared to the normal games' music.
Battle Revolution and the likes are another good example, since the normal hand held games don't let you battle it out in a, well, cinematic way like that.
I didn't like Pokémon Ranger though. Never thought the stylus capture thingy was fun or good.
Interesting thing is that Pokémon Ranger setting and world is part of the anime canon, but not PMD. It's like PMD is a whole different dimension/world/canon/saga/whatev. Playing as a Pokémon yourself, that's what Pokémon could have been, and now they've turned that into what Pokémon is. And I love it. Shows that there are no limits to creativity.