With all due respect to Mike Mearls, he is wrong. The action economy in 5th Edition is beautifully designed, and I wouldn't change a thing about it.
I would never explain that to a casual player because it's wrong.
I get my reaction back on my turn. If I cast a spell and it gets countered I can use my reaction to cast counter spell.
But, it does get wonkier.
On PC's Turn, PC casts a bonus spell and the Opponent casts Counterspell. The PC uses his reaction to cast Counterspell of the Counterspell. PC's turn ends. Opponent then casts spell on PC, but, PC cannot counter spell because he's already used his reaction on his turn and it won't refresh until his next turn. It can be a bit confusing.
To be fair though, this is a pretty rare thing to come up.
You can't do the part in bold. It's illegal to cast another spell on the turn when you've cast a bonus action spell. Dausuul is correct.
Both wrong. If both spellls were cantrips you can counterspell IIRC. Now I have to reread the phb as I could be wrong.
http://www.5esrd.com/spellcasting/ said:A spell cast with a bonus action is especially swift. You must use a bonus action on your turn to cast the spell, provided that you haven’t already taken a bonus action this turn. You can’t cast another spell during the same turn, except for a cantrip with a casting time of 1 action.
You might want to check the rules BEFORE loudly proclaiming other people to be wrong. In this case, you're wrong.
Counterspell is not a cantrip with a casting time of 1 action, therefore it cannot be cast in the same turn as a bonus action spell.
Fine. Weasel out of it.
And personally I am not attached to the bonus action. I'm just not willing to get rid of it, just for the sake of getting rid of it. His current suggestion of "Just make a bunch if individual actions" doesn't sound like a good solution to me. Instead of learning a couple general rules, you will need to learn potentially hundreds of separate special rules, some with their own little corner case.
Here are so other suggestions.
1. Don't get rid of bonus actions, but reduce where not needed. Two weapon fighting seems like one of the biggest offenders*.
2. Make a clear list of actions and bonus actions. Include a chart in the book. Make space on the character sheet to list the action type.
3. Eliminate special exceptions. Do you really need to limit casters to a cantrip with a bonus action spell? I have yet to see a really broken combo. And it will just burn you spell slots faster.
*The real problem with removing the bonus action from two weapon fighting is that they added a style and a feat to boost it up to make up for the fact that it requires a bonus action. Now if you take it away it is unbalanced. If you just tone down the power of the style and feat you can get rid of the bonus action requirement and it is fine.