Just sunk a couple of weekends into Solasta. Prompts are great imo, but Solasta's aren't perfect. Here are a few things BG3's prompts should avoid.
Too much text. It's fairly short for Shield ("Giant Spider is attacking Tav, you can cast the Shield spell to block the attack") but even that sentence could be edited down. I can't find the full text for the Counterspell prompt at the moment, but it's far longer and buries relevant information within repetitive phrases. This is all good for explaining what's going on the first time a prompt happens, but the way the information is presented could be cleaned up.
The camera can't move while the prompt window is active. (I think. It may be down to user error). Some reaction decisions require a measure of battlefield awareness; looking around helps with that.
Simultaneous reactions aren't intuitive (to me). Classic example: an enemy exits the zone of control exerted by two of my PCs at the same time. The prompt window shows both of my PCs able to make an Attack of Opportunity, but they can't both take a swing. When I pick a PC to react, the window closes and the other PC does nothing. Positive : grouping reactions in the same window; negative: having the grouped reaction window eat one of my PC's reaction.
The prompt will occasionally pop up even if you can't take the action. (Wizard casts Magic Missile on target who responds with Shield. Prompt comes up for Counterspell on Shield. I click 'Yes', but the Counterspell doesn't happen as Solasta won't let you cast two leveled spells a turn.) This is more bug territory than anything else, but any reaction system relies on a robust system of conditional checks. Make sure it works, please.
That last one may not be too helpful... It's hard to be in a helpful mood when Larian's first message (22 into months into EA) says “[they] aim to interact with [us] as much as [they] possibly can”. This statement may not technically be a lie, but no fact corroborates it.