Hey, seen a few of your videos from time to time and they're a nice watch, thanks for posting looking for feedback, I hope some of this helps.
1. Quality sounds fine, and personally, the content you speak about will almost always supersede the quality of the microphone.
2. The commentary was interesting, but generally I'll describe to you the two things I find most motivating to watch a live commentary. I like commentary videos where the commentator is either telling a story or talking about something they experienced, or discussing game mechanics/strategies/metas and providing their insight on a matter.
3. I guess mostly, getting better at the game will help. What makes a lot of commentaries constantly interesting is the combination of gameplay thats nice to idly watch while the commentator talks about something. Also, like stated above, I struggle being entertained by these sort of videos where the commentator doesn't have a topic/story that they'd like to discuss. Honestly, I think it would be interesting to hear your thoughts on strategical aspects of the game, weapons, etc, because you are untarnished (for the most part) by the metagames of tf2.
Best of luck!