Yeah, definitely check your audio levels when you do these videos. I have an audience on Twitch that I rely on for audio settings (and I thank them for helping me do less of an assy job doing streams), but you'll want to find some way to preview if you're going to process them (and when you get your audio settings just right, find a way to save them as some sort of template or default setting).
I don't watch many Let's Plays (usually I watch ones that are pretty much novelty streams, like Retsupurae or the Shiddy Kat Wifestreams or streams of games that are terrible), and these observations are pretty off the cuff, so please take this with a grain of salt. I largely take a crack at commentary during my Let's Plays, but I'm not all that good and I prefer to let the game speak for itself. That's why I don't post my Let's Plays on Youtube, because I kind of feel like I'm a big boring dummy who doesn't really have anything insightful to add to the game itself. But some people enjoy watching me play video games! I don't know why! But they do!
Anyway, I feel like your commentary's all over the place - that you're trying to fill up the video with as many words as you can, and as a result, it feels like you're trying to get in the way of a game you're playing to show off. Undertale is great, and your enthusiasm is infectious! But the thing is, you gotta remember less is more. Work within the game's ebbs and flows - I feel like you got in the way of the introduction to Undertale with your commentary, and that opening scene is absolutely important when it comes to setting the tone of the game.
I don't know if that will help you or not. But I recommend studying what your favorite LPers do when it comes to games, nonetheless.