I actually did this recently so I have a clear memory of it lol :) I thought Red's inclusion was fantastic, especially as the Johto protagonist has just swept Red's region it makes sense that the two have a face-off :) I'm also glad that they kept him as a silent protagonist :)
I was a teensy bit underlevelled the first time I faced him so I found it difficult, raised my Pokémon a couple levels each and faced him again and lost out to his Blastoise. The third time was third time lucky, I was able to use the same method I had the second time around except more effectively lol :)
Pikachu was a breeze, I had a speedy Nidoking with Quick Claw so I used an effective combination of Flatter and Earthpower which did the trick :) Lapras was pretty tough, it took out a lot of my team with Blizzard. Snorlax wasn't too bad, I had a lot of hard-hitting moves so it went down easier than the Lapras. Charizard was the easiest for me along with Venusaur. I faced Venusaur with my Venomoth and the Venusaur wasn't able to do a lot of damage to it, so I was able to use that time to restore the rest of my pokés for facing Blastoise haha :) Blastoise again proved to be the hardest for me to take down, needing a combination of poison, confusion, Petal Dance and more lol :)
Beating him was such a satisfying feeling, it was almost like Red was the main rival of the game the feeling was that strong lol :) I'm glad the game rewarded you for it as well with the Kanto/Hoenn starters, it was a big achievement and deserved recognition :)