New user, like the game and interface, willing to spend a bit o cash, had a 'bad' experience spending money.
My experience:
Found MTG arena recently, have used Duels in the past, long time casual irl and online MTG player. Love the game, interface much improved over other digital MTG, great stuff, thank you.
I wanted to expand my card base so I bought a bundle w/gems and spent the gems on 15 packs.
In my excitement just clicked the button, 15 packs. Realised I'd bought 15 packs of Zendikar Rising. I likely might have chosen that option anyway, but looking back on my automatic reaction I think I expected there to be a screen asking me for the details, rather than choosing it from the prior screen.
My next thought was that there would probably (hopefully) be an option on the Packs screen to open multiple packs at once. So on the Packs screen there was a button labeled Open x 10. There it is, I thought. Clicked it.
Now rather than having 15 packs worth of cards, I have 5 packs worth of cards, and 10 mythic rare/legendary cards. That's not what I wanted, and I don't think it should be that ambiguously labeled.
However, 10 Mythic Rare/Legendary cards is pretty awesome and I want to keep them. I just think the option should be far more obvious about what it is you're about to do - spend 10 packs on 10 cards with an increased rarity value. Nothing I saw indicated that that was what I was spending my money on.
Thanks, JTHM