First

Initially I rolled my eyes, but this actually quite the clever joke.

Ah, the spell components, well played.

So they specified that the character is “incapacitated” now. Stopping bonus actions and reactions, I’m guessing?

The grammar in the new PHB is strange. “That action can be used to take only the […] action.”, should be “That action can only be used to take the […] action.” And I'm not a native speaker…

Quote from Aarndal >>

The grammar in the new PHB is strange. “That action can be used to take only the […] action.”, should be “That action can only be used to take the […] action.” And I'm not a native speaker…

Both versions are valid English grammar and mean the same thing in this context.

Lickety-split

Because candy is dandy but licorice is quicker-ish?

oh, no, I had to look it up. It actually makes you GO faster. 

If I cast this on the barbarian, then let him out of the fortress to go off (say 90-120ft) to fight the boss's monster... will this spell hold while my friend is out of sight and beyond 30 ft? (providing i'm still concentrating)

yes, the spell will hold as long as you hold concentration; you could send the barbarian to the hells and they'd still be hasted until the spell ends

What about horizon ranger?

Quote from Jreamer >>

Because candy is dandy but licorice is quicker-ish?

oh, no, I had to look it up. It actually makes you GO faster. 

 Cause sugary foods gives you a quick boost of energy followed by a "crash," which is basically what Haste does.  

Ah, "Attack (one weapon attack only)" changed to "Attack (one attack only)." This means Valor Bards, Eldritch Knights, and Bladesingers can cast a (non-Eldritch Blast) attack roll cantrip with that action.

Though, if you are any of those people, you'll probably be casting True Strike, Green-Flame Blade, or Booming Blade - which already worked with the old wording. At least, I thought it did, and now it definitely does.

If you don't think this works because it says "one attack only" instead of "only one attack," Eldritch Knights still bypass this with their wording of War Magic - Fire Bolt is one attack as much as a standard weapon attack is in this case. I think it's clear that the intention is for 7th-level Eldritch Knights and 6th-level Valor Bards/Bladesingers to have equivalent Extra Attack features.

if you still don't think it works for the full casters because Haste overrules their Extra Attack feature, you must also think that they have to make both attacks in a non-Haste Attack action for one of them to be replaced with a cantrip. The feature says you *can* attack twice instead of once, not that you have to. What, if you decide to only make one attack - it can't be a cantrip? Say a Valor Bard is holding two daggers and casts True Strike as part of the Attack action, which triggers the Light Property. They make their Light attack, which kills the last enemy in their range, so they end their turn. Well, they didn't use the second attack of their Attack action, so they must've had to cast TS with the Magic action! Then how did they make the Light attack?

BG3 enjoyer and new DnD player here. Can I Haste the Tempest Cleric and Call Lightning twice (as in BG3) or is that video game magic only?

what if you persuade an enemy into being the target of this spell and then imidiatly breaking concentration.

Quote from Iroh115 >>

BG3 enjoyer and new DnD player here. Can I Haste the Tempest Cleric and Call Lightning twice (as in BG3) or is that video game magic only?

 Both casting and re-activating it are Magic actions, and this spell's extra action can't be used to take the Magic action. 

Quote from vuurdraakje468574920 >>

what if you persuade an enemy into being the target of this spell and then imidiatly breaking concentration.

Sure, but you can do the same thing with Command for a lower-level spell slot.

Except it doesn't allow for any magic actions.  Which is exactly what a cantrip is

It isn't exactly what a cantrip is. Those characters are casting a cantrip as part of the Attack action.

Technically this is better than the 2014 one since it gives the actual Incapacitated condition meaning immune creatures can still take actions.