I've always thought the mindgame was the most challenging and the most fun part of improving in Smash..
What was so great about smash was that there were two levels of development. Actual experience and tech skill. Mind games do not really exist, it's just the art of reading your opponent and getting into a better position than him.
Tech Skill is the ability to WD, L-cancel, and do character specific techs consistently.
You could not be sucessful in melee without doing both. My friend is the perfect example. He can double shine 26 times in a row (this is nearly impossible), but he is really predictable cause he only plays the same people over and over again. I'm nowhere near as technical as him (i don't think I even l-cancel consistently) and I beat him by a lot (even when I play his Fox with my Ness).
You need to practice tech skill in order to pull off crazy stunts. You need experience in order to apply those to actual battles instead of the lvl.1 cpu. In melee it's a mixture of both. Being able to WD spam doesn't mean insta-win. You have to be able to apply it.
Not only that, but L-cancelling was not even a glitch. It was put into melee as it was discovered by Nintendo in 64. L-cancel also made a lot of the slower characters viable in tournament play and allowed for some awesome combos. It also was a counter for shieldgrabbing by Marth and Sheik, whose grab-ranges were larger than most attack hitboxes.
Also, they kept a glitch callled float cancelling which gives Peach 4 frames of lag after she lands and arial she started while floating. This is obviously extremely broken and was kept even though l-cancel is out. Wanna know what happened with a character that did this before:
http://youtube.com/watch?v=E2baExmi71g
Another major gripe is that lack of l-cancel slows down gameplay even more. What is more interesting: a fast paced game full of combos, or a slower one that consists entirely of shield grabbing and camping.
tl;dr: tech skill allows you to be creative, experience allows you to use that creativity. Pros will still **** noobs, it's just that pro vs. pro matchups might get long and boring.
Ironically Sakurai nerfed arial gameplay instead of boosting it with the changes he made >.>
Edit: Yes I know I haven't even played the game yet, but if it turns out like this then it'd suck. We were lucky that melee was so technical cause it was very buggy. Since Sakurai spent a lot of time on this game, this decreases the chances of finding helpful glitches that could help in battle. The fact that Falco can cancel his running attack into an up-smash makes me hopeful, but that still isn't very useful, especially for the rest of the cast. Another thing I didn't understand was why he nerfed Fox and Falco a lot, but did not nerf Peach, Marth, or Sheik noticeably. In fact Peach has a major advantage right now in that she has the fastest arials in the game. Ironically Fox and Falco were really techy characters.
Edit 2: Another thing people fear is that the game will turn out similarly to smash 64. Some characters were so blatently overpowered that all you had to do was memorize the 0-death combos. All the matches had the same outcome, and matches get boring to watch after they all do the same thing over and over again. In melee there was greater diversity not only because there were more characters, but because there were more techs (and thus more playstyles/options/things to do for a single character).
