Watching [Johnson Plays], the voice is smooth and comes accross very well. You speak low and that is fine.
I think you use 3 audio inputs (game, voice and post-prod sound effects or live samples). In terms of relative volume, your FX are too loud. It's possible the game effects can be raised.
As a general rule, the viewer adjusts his own volume on your voice. Then you consider the volume range. In radio, they use a lot of machinery (compressors, limiters) to keep the volume variations within 8dB. It produces some distortion but it also means people with a crappy sound system or a car engine running can hear it all.
So, maybe you can use this rule of thumb to adjust your relative volumes. (I don't think you've got access to heavy machinery.)
Voice is your 0. Game is your -4dB. FX, I dunno, lower than the voice but probably higher than the game's volume.
Your overall voice volume can also probably be raised. People (with crappy systems) can more easily tone the volume down than they can raise it.
You could open a random mp3 file for reference and use it to adjust/normalize the final volume you want.
It can take a little while adjusting those settings properly but then it's done once and for all.
Hope that helps, good luck, it's a good and fun exercise to speak live into a microphone
edit : it's possible what I took for your own sound effects are game effects. I don't know what the source is. If they are game effects, those are a lot louder than both your voice and the game's atmosphere. Not sure if there are several in-game audio levels.