Skipping a few reviews: a Team Galactic episode, a Chingling episode, and Dustox's farewell. The first and last of those are ones to watch, but my knowledge of Team Galactic is quite lacking, and my life experiences don't allow me to really understand the Dustox episode on a personal level.
This episode sort of works, and then it does not. I think, if the writers had put a bit more effort in setting up the main points, the episode could have been a masterpiece, since what they wanted to show is a good idea: Pikachu near death, and Paul's suggestion that Pikachu should evolve. But, well, the way Pikachu gets near death is sort of...not right. Pikachu takes a close range Hyper Beam from Raichu in a battle, and that's what puts it in critical condition. However, if pokemon battling can be THAT dangerous so that the life of a pokemon is endangered, well maybe pokemon battles shouldn't be allowed in the first place.
I also don't think a good reason is shown for why Pikachu is upset with Raichu's trainer/Raichu. The reason for why Pikachu meets the trainer in the first place is for sure not very creatie: at lunchtime, Piplup knocks away some of Pikachu's pokemon food, and both pokemon chase after the morsel until they are out of eyesight of Ash and the gang. The trainer finds Pikachu and wants to catch it; Ash comes along and stops him. Then the trainer offers to trade for Pikachu, which Ash refuses to do. That should be the end of things.
But Ash notes Pikachu wants to battle Raichu, and so he challenges the trainer's Raichu to a match with Pikachu (I liked how Ash seems so much older than this guy; the guy tries to bait Ash into putting Pikachu's ownership on the line in the match, but Ash firmly makes it clear that this match will not be about that-Ash is the one setting up the terms of the match, dictating the pokemon to be used and that this is just a normal match). However, why does Pikachu want to battle this guy? I don't think he did anything wrong, and the fact that he wants a full evolution set is not exactly evil: Morty back in Jhoto used an evolution set of Ghastly, Haunter, and Gengar at his gym. I don't really see why Pikachu has so much anger; it can't/shouldn't be just b/c Raichu is its evolved form. Ash and Pikachu have been traveling a long time; they must have seen a bunch of Raichu. And even if this Raichu thinks its better than Pikachu, it's out of character for Pikachu to just pick a fight for no reason. Going back to the Luxray episode, Pikachu knows Luxray doesn't like it, but Pikachu doesn't make the first attack. It's only wary and on guard in case Luxray does attack it. The same thing can be said for Paul's Elekid/Electabuzz. Pikachu doesn't attack unless it's been attacked first.
So, ignoring why Pikachu is in the pokemon center near death, the scene itself is very touching. Of Pikachu's memories, the two surprising ones for me were Pikachu fighting a Gyrados pre-Hoenn period (my guess would be against Clare; sorry, too lazy to search the thread to make sure-but I do remember watching that gym battle and thinking Pikachu was impressive for defeating a Gyrados) and, not quite as surprising, Pikachu's victory against Brandon's Regice and Ash earning the final frontier symbol. The latter is very interesting for me, b/c one thing Sinnoh has done very well is that it's made the Battle Frontier seem like something very important for Ash and an impressive achievement overall; it's the main reason why I think Ash is as mature as he is right now, and why he has a legitimate shot of winning the Sinnoh League. Ash's result at the Sinnoh League is going to have a big impact moving forward, not just for how Sinnoh is viewed, but also in how the Battle Frontier is remembered, whether as something prestigious or something that's pretty much a filler (like Ash's Orange Islands victory).
Ash's single tear when he sees Nurse Joy try to get Pikachu's heartrate stable (I think) is something that I'm always going to remember. It's something more moving than anything he could have said. Just the way the tear forms, as he sees Nurse Joy become deadly serious and decisive; I've never been in a situation like that, but I could feel something of what he was feeling. That's the failing of this episode, really. It starts out with kids logic, that people will accept a Pikachu vs. Raichu battle, no matter how it happens. But then the episode reaches a part like this, and it's not kids logic at all anymore. This is a very serious scene.
Pikachu survives, of course, and sneaks off at night to do some training. Ash and gang search for Pikachu, with Ash running off from the group to find Pikachu on his own. And while he's running, this is one of the few times that the writers give Sinnoh Ash's direct thoughts at an emotional moment like this; Ash can't understand why Pikachu would leave w/o him, since they've been through all tough times together. This reminds me of a scene back in the maze episode (pokemon are separated) where Ash tells Pikachu they need to find Dawn and Brock as he imagines they could be in trouble (he pictures Dawn being attacked by Onix), but when he gets separated from Pikachu, he slumps down in wishes Pikachu were there with him. Sinnoh Ash is often so composed and confident, but I like how his friendship with Pikachu shines through when they're separated (and by that, I don't mean by TR thievery; I think they're both used to that by now).
Now for Paul's appearance. The way he shows up here is a little like the way Zoey has shown up a few times, as Paul observes the match b/w Ash and the Raichu trainer and advises Ash to evolve Pikachu. I think Paul's appearance here is more in character for him than the Gligar episode (where Paul just wanted Ash to stay out of his way), since Paul is again showing a level of respect for Ash in giving him advice (and he even watched the battle!). The next morning at the pokemon center, Ash and the group see Paul as he's about to leave. Ash shoots Paul a look (a look!) that surprises Paul at first; Paul then closes his eyes and walks away. I'm pretty sure that look was Ash's way of telling Paul to come watch Pikachu's rematch with Raichu, b/c that's what Paul ends up doing in secrecy. Pikachu wins, using some admittingly weird rolling techniques (but considering how far food rolled at the beginning of this episode, maybe not so weird), and even limiting the damage from Raichu's Hyper Beam using Thunderbolt (reminding of when Charizard used seismic toss on Blaziken with Blaziken surviving only b/c it used flamethrower to soften the blow). Paul walks away after seeing the battle with a Hmph!, but the fact that he watched at all and saw Ash win using his own strategy and not evolve Pikachu is a sign of respect. And no, I don't think that means Paul was wrong to say what he did, and this doesn't change his own personal style. B/c before one of his battles with Ash, Paul uses the ten days he has to train to evolve one of his pokemon, and that pokemon plays a reasonable role in that match. But what Pikachu's victory in this episode does show Paul is that Ash isn't wrong either; connecting with your pokemon can and does work.