There were 3 main parts to this 50 minute first episode.
1) The Upper Moon Meeting - Demon Slayer has always been amazing in the character design department. Every character is always so masterfully crafted; with designs that perfectly suit the character and always look so aesthetically pleasing. The Upper Moons are no exception. This meeting takes up about half of the first episode, and through amazing cinematography, and ufotable's legendary blending of 2D and 3D animation, incredible amounts of tension were built into every interaction. The splendor of the Infinity Castle is a sight to revel in, and I'm sure we'll be seeing much more of it in the future.
2) Someone's Dream - Tanjirou dreams of a past ancestor and his meeting with the mysterious swordsman, who the very thought of continues to haunt Muzan. Tanjirou's ancestor, Sumiyoshi, is the spitting image of Tanjirou, even wearing the same pattern on his haori. The swordsman seems to be very somber and upset about his circumstance. I hope the story will further develop his character and his importance to Tanjirou.
3) Recovery and the Journey to the Swordsmith Village - Plenty of adorable scenes and character interactions in this episode. One of my favorite aspects of Demon Slayer is how endearing the characters and the way they interact with each other are. Kanao was a standout this episode, and Inosuke is as hilarious as ever. You can always feel how much Inosuke looks up to Tanjirou and views him as his own big brother. Can't forget Gotou's reappearance! Tanjirou finally reunites with Genya, who still doesn't like Tanjirou at all. I'm hoping they grow as close as Inosuke and Zenitsu have to Tanjirou. He seems like a really amazing character and has an amazing aesthetic. We also got to see Mitsuri grow really close to both Tanjirou and Nezuko, while also leading them on a little treasure hunt.
Overall, this episode really pushed forward the plot, while also developing several characters for both Demons and Demon Slayers. This was a great start for me. This story is masterful at setting the tone, both comedic and serious.