I love this series. They are puzzle games, but I'd say the biggest draw (at least for me) is the philosophy. The puzzles give you something to do on your journey, but they aren't the real thing you take away from the games when you're done.
That said, I found 2 much easier than 1. If you want challenging puzzles, the DLC for 1 is really where you want to look. All of this series is worth playing though. My biggest disappointment is we probably won't get a 3 if I had to guess. I do hope we get other games that ask the player to think outside of the game though. I love philosophy, and this series prompts the player to think about so many good topics.
Funny thing is while I'm decent at platforming I'm terrible at pvp. The most fun I've had in pvp was a medic for my brother when he was a heavy in TF2. Has so much fun keeping him alive while he was mowing people down. Need to do that again some day....