OS, just my opinion, but next time don't have a "guiding question," cause this thread seems more of a discussion of Metaknight's tornado than anything else ^_^'' Anyways, I just wanted to post some general thoughts about Metaknight in general before this thread finishes.
First off, his B attacks are incredible. Up B is a great KO move at times, and has awesome range when you know how to use it. Plus, his attack out of his glide is ALSO a great KO move, and if done correctly won't leave you open at all. His forward B, like others have said, is a great shield poke (and can also work as an anti-projectile spam move at times IMO), and he isn't open at all afterwards if you simply point it into the ground right before it ends. His regular B requires no further explanation as the attack is just incredible. But MK's down B seems to be his weakest special. The uses are limited to mindgames, and the attack doesn't even KO as well as most of his other moves. Plus, he is completely open after using it, as well as the move taking just a little bit too long to come out so its easily read. Although its my favorite of his specials, I don't expect to see this attack to come out too often.
His ground game is also superb. His is fast as hell, his dash attack is great for popping your enemy up, his running up-smash kills spotdodges, shields (to an extent), and catches the opponent most of the time if they airdodge trying to land on the ground. His grabs are awesome, his tilts have range and speed, his neutral A is surprisingly good, his downsmash is fast and powerful, and his forward smash, although hard to time, is also very powerful when used correctly.
MK's air game is good, but IMO its not incredible. He has plenty of ways to combo you in the air, but his KO ability isn't stellar with his aerials, although I've seen his up air and down air KO rather handily if they are rarely used throughout the fight.
In my opnion, MK is probably the best character in the game right now. His biggest "disadvantage," KOing, isn't as bad as it should be because his down smash is very easy to land, and quite powerful. Although, I think we'll be able to figure out how to beat him down the line, and he won't be quite so good after a little while (but he'll still be near the top).
Now, to beat MK, I've found a few solutions to work quite well. Of course, like others have said, MK is really vulnerable to projectile spamming. Other than that, I've also found the little bugger to be ridiculously easy to kill off the top with alot of characters. My personal favorite being Snake's up/down tilts or his up air. Each of them can simply decimate MK.
This may be common sense to most people, but I just want to point this out for the few who don't know. In my experiences so far in the game, I've noticed that every character is either a "heavy" or a "light" character. But I'm not solely talking about character weights. A "heavy" character dies to the sides much easier, because they either don't have a good enough recovery, they are easily edgeguarded, etc. But "heavy" characters will live until ridiculous percentages if you try to KO them from the top. But "light" characters are different. These guys have recoveries that are ridiculously good, so they are just simply stubborn as hell if you try to take them out from the sides (although they aren't as good at avoid side KOs as "heavy" characters are at avoiding top KOs). And if you want to take them out, just hit them upwards and watch them fly at 80%. I know this seems like the most obvious thing in the world, but I've found these distinctions to be much more clearly defined in Brawl than they were in Melee. In Brawl, Top vs Side is a BIG difference due to the different aerial styles and the variety of anti-air attacks made for KOing off the top. I've come to realize that my playstyle is drastically different for characters who are vulnerable to top KOs vs characters vulnerable to side KOs, and learning which category each character falls in (and to what extent they do) has really helped me counterpick and what not in tournaments.