The thing that gets me about these missions is only about half of them actually feel right. For how much I hated it and groaned when they did it in, I begrudgingly accepted it as it made sense, storywise, in Prototype. I still grumbled to holy hell the whole time and shot through the levels as soon as possible to get it over with though...
It always pisses me off though, always. If you want to challenge me, challenge me. Don't dumb me down so you can pretend to challenge me because anybody can kick a kitten.
As far as preview of powers go, I love and hate them. I like getting a feel for what I will get but I also loathe having the surprise ruined. Sure the degrade in power in Assassin's Creed was tolerable and made sense for the story, blah blah... But why ruin the surprise?
It is one of the reasons I am looking forward to Assassin's Creed 2. Instead of starting in the middle of a guy's career and getting dumbed down for penance, we get to be at the beginning of his career and work our way up. It makes me feel like I am part of the story from the ground level instead of some middle manager coming in after the company got off the ground, so to speak.