One thing I've noticed that both MTG and VS seem to have in common, that I think many many players dislike, is the introduction of a new mechanic every set, and then not using it alot throughout the next set. Instead I think it would be much better to not release as many new mechanics, but actually USE the mechanics the game has in more sets.

well this would be a good idea if the cards werent based on chars that have this mechanics. you can throw all the mechanics at us at once.

I think it's because some mechanics turn out better than others. Leader, for example, was introduced in the Avengers set, but has seen extensive use in JLA as well, because it is a good mechanic, while Evasion, which is rubbish, hasn't really been seen much since it was introduced.

What I worry about is the complete lack of Willpower in Marvel, which puts any Marvel based deck at a disadvantage to decks with Battle of wills and such.

You may be right, in the instance of the new Mutant mechanic, which I don't see being used much outside of X-men, unless they introduce other similar elements like Robot, Undead, etc, which would make older cards completely obsolete.