I'm not really sure if I can say anything too insightful about this episode that hasn't been said (and hopefully, by writing this statement, this makes it okay-lame, isn't it?).
Okay. I think this is the toughest gym battle Ash has in Sinnoh, not just b/c of how strong Lucario is, but b/c Maylene does not make any mistakes in the battle. I think the seriousness of Maylene and Lucario in this match is best summed up by the part of the battle where Lucario is enjoying itself using Bone Rush to deflect Buizel's Sonicbooms, and then when Ash/Buizel in turn show off by using Sonicboom to defend against an onslaught of Aura Spheres, Lucario sneaks in and uses Force Palm. Maylene sort of gets ripped off by the gym challenge rules, as Ash first switches out Staravia and then later Chimchar to get rid of the confusion effect from Meditite's Confusion attack. This wouldn't be so bad for Maylene (remember Ash really bent the rules when he fought Anabel back in the Battle Frontier, as he recalled Corpfish and then sent it back out) if Ash didn't get fortunate in other areas as well, with Buizel learning water pulse and the rain. Even so, Ash still almost loses, and he has to push Buizel urgently a few times in the match to stay in it. The biggest reason why Ash ends up in such a pinch is that Chimchar sort of lets him down; I get the feeling Ash was hoping for Chimchar to deal a bit more damage to Lucario, judging from Ash's reaction when recalling a fainted Chimchar (Paul's pt exactly about Chimchar; no blaze, no use for it. But Ash is sympathetic to Chimchar, and really there's no wonder that Chimchar is so much happier with Ash, as Reggie pointed out a couple of episodes. Speaking of Reggie, too bad he's not here to watch). Ash realizes he's in a bind now that the match is reduced to Lucario vs. Buizel, or power vs power, which Buizel is probably not going to win. Ash really gets reduced to trying to keep Buizel on its feet, and unlike most other gym battles, he doesn't come up with a super strategy; Maylene doesn't give him any opportunity. Ash does use Dawn's contest Aqua Jet to overpower Lucario's defensive Metal Claw, but Maylene just upgrades to using a defensive Force Palm, which brings that match-up back to a tie. With Buizel's Water Gun being overpowered by Aura Sphere, Buizel really does not have any option to attack before it learns Water Pulse, which is a draw power-wise for Aura Sphere).
In the end, Ash does take advantage of his luck with his finishing move, a water pulse/aqua jet combination which he had to have come up with on the spot. It's really nice, and more interesting than many water type contest moves I've seen.