I was on Mirtazapine for around 7 months from 15 to 45mgs and agree 30mg seem to give the best results for mood and sedation. I have awful insomnia, anxiety and mood issues from time to time. Went 3 days without any sleep at all when they tried me on citalopram!!!!
I had pretty vivid dreams too, also amazing white zaps of light in front of my eyes when I initially closed my eyes and settled down to go to sleep... Used to look forward to this free "light show"!
Now free of any depressants and using diazepam for sleep and GAD. Only on 5mgs at night and seem pretty stable at the moment... for me anyway!
Good luck!!!!!!!!!!