*cracks knuckles* Here we go.
Pikachu, In my opinion, deserves to go up at least 1 spot in the tier list, above Dedede. He has pretty good match-up ratios with the top tiers (45:55 with MK, 50:50 or 55:45 with snake, 45:55 with Diddy, 65:35 with Falco, 50:50 with IC, 45:55 with Marth [will explain those 2 later], and 60:40 at least with D3). His CG alone obliterates a lot of characters (Falco, D3, Bowser, DK, Snake, Fox, Sheik, Charizard, Ganon, Falcon) and he has a very potent approaching tool in his T-jolt. Once Pikachu gets in he is one of the most effective damage rackers in the game (fair combos, low % grab combos or CG) with 3 applicable moves that jab lock (D-tilt at low %, QA at all %s, and Jab at mid-high%). Pikachu has the speed to effectively keep a good pressure game and has one of the best space control in the game with his T-jolt and thunder.
He has one of the best recoveries in the game and one of the better edge-guarding games (More for damage than for gimping, but that is a potent ability as well). Even off stage he can manipulate where the opponent has to go with his T-jolt, making them waste their DJ or stay out until it passes.
Pikachu is also unique on the ledge. On the bad side, Pikachu has 12 less frames of invulnerability on the ledge. On the good side, that allows Pikachu to get off the ledge 12 frames earlier, making grab ledge-> fall of ledge attack a good and easy way to edgeguard. The bad side is that for characters that need to be edge-guarded by using the ledge invulnerability (Diddy Kong and Marth come to mind), Pikachu has to have near perfect timing to gimp them. Pikachu also has one of the best ledge pressuring games. If people are refreshing their invulnerability, ie Marth ledgedrop fair up-b, he can shoot a T-jolt down there and maneuver space so that Marth will either get hit or have to miss the edge which allows for damage. He also has D-tilt which hits people off the ledge and a powerful F-smash for ledge reads (Roll, get up attack, normal get up). If Pikachu is scared of his opponent ledge-jumping (Not ledge hopping) he can FH a T-jolt, land, and react accordingly. It is really easy to control space as Pikachu.
Not only does Pikachu have a good running speed, he also has the maneuverability of Quick Attack Cancel, Pikachu's ISJR. It allows Pikachu to catch up to his opponent extremely fast, as well catch people's landings with a QAC nair. The fact that QA has so many angles can allow Pikachu to recovery amazingly as well. Instead of being forced to the ledge or to blatantly overshoot it and fall with lag like most characters have to, Pikachu can QA from offstage onto a platform, and then QA farther onto the stage to get away from the edgeguarding.
Pikachu also has a very good momentum cancel in his uair and skull bash. If you skull bash to momentum cancel, you will rise up slightly, but it will completely get rid of horizontal knockback. For vertical knockback, Pikachu's Fastfall is also pretty good so he will survive much longer than most people in his weight class. That doesn't mean I'll be surviving DK's D-smash at 110 though...
Pikachu's most glaring flaw is his lack of spacing. His longest range moves (aside from projectiles) are D-tilt and F-smash. However, in my experience I never really worried about that because of all the ways Pikachu can get in. He can run with his T-jolt, QA mindgame in (Which I am starting to do more) and just using his speed and aerials couples with T-jolt can be devastating to people who don't have Up-b OOS with invulnerability.
Pikachu's kill potential is pretty good IMO. Not the best like Snake's or DK's but very solid. F-smash is a strong killer, as is thunder (Blue). U-smash and U-tilt are fairly good on their own, killing mid weights at ~120% and ~140% respectively. Thunder drops these numbers by a good 20%, making 100% danger zone for many characters.
Pikachu's match-ups are really really good. Although a lot of Pika's don't think so, I think that Marth isn't Pikachu's worst Match-up and neither is Metaknight. Pikachu's hardest Match-up is Lucario. He has an extremely effective keep-away game, can outcamp him, and forces him to approach. When Pika does approach, Lucario can F-smash or fair to keep him out. Fair cancels out T-jolts as does aura sphere, and Pikachu doesn't have any sort of anything from grabs. F-throw U-smash, guaranteed on nearly every character, does not work on Lucario, and neither does D-throw nair. Because of this, Pikachu has a hard time damage racking.
Even after Pikachu gets the damage in, it is hard for Pika to get in the kill move. Lucario can effectively keep him out, and the only option is to get little hits and hopefully hit him off the level. Lucario will normally survive until at least 120%, and that is when aura is really scary for a Pikachu. Maybe it is because of my match-up inexperience and the fact that I basically only played the best Lucario, but the match-up seems horrid.
Marth really isn't that bad. SH double fair, Marth's normal keep-out game, is very punishable by Pikachu. He can shoot T-jolts to pressure Marth, and then shoot them at Marth's feet to make marth either shield or hit them. That leads to pikachu being able to get in with a FF Fair. If the marth wants to up-b, Pikachu can shield and punish. If not, Pikachu can get a nair in or a grab. Once Pika gets in...it is unfortunate for Marth. Pika can also just camp. Even though Marth can cancel the Jolts, it'll constantly have marth swinging away, and eventually he will slip up and let a few through. If not, the pressure is still nice. Pika can also punish a shielded DB with nair and grab. F-throw U-smash doesn't work at 0, but it works at 10% until like 30%. Still a nice damage racker.
IC...I don't understand why people think this is a bad match-up. Maybe because he can't space his melee moves? I honestly don't know, but I have always seen this match-up as even. Pikachu can completely molest nana when they are separated. If D-smash separates them...nana is dead. Because of her AI of always returning to popo, she will run right into thunder. Her DI will set her up into another thunder and possibly a third thunder if necessary. FH nair works charms on IC fishing for a grab, and T-jolt can skip over ice blocks and obviously goes through blizzard. Pikachu also has a very potent edgeguarding tool against up-b. WHen nana goes and grabs the ledge, pikachu can fall off either with a nair or bair and hit popo on his way up, which ends the stock. For Squall, Pikachu has Thunder to hit them out of it. If not fishing for grabs, Pikachu and Ice Climbers have about the same spacing with their attacks (Hammer vs tail). Pikachu's are much faster and can combo much better.
So yeah Pikachu should be 7th or 8th. He should definitely be higher than he currently is.