It's been 15+ years for me (although with lots of on and off), but if you're used to living with ADHD, it can feel like a fog is being lifted. You can suddenly hold more in your head at once and don't have to mentally "drop" a thought to be able to process other things. It's like slotting in an extra stick of RAM.
The meds probably have that effect on anyone, but it's profound if you've been working with a deficit.
Back in the 70s & 80s kids were, on-average, given 30mg instant release of Ritalin a day to start. These days they've cut that starting dose down to 5mg 2x a day for IR and the long acting is 10-20 once a day depending on the child's weight.
Dosage back then was also determined by severity of "undesired" symptoms instead of other factors like body mass and how well a lower starting dose is performing.
When I was a kid I was struggling in school so my parents put me on some nasty amphetamine derivative which I stayed on until my mid 20s. It didn't really make anything easier it just made boring things seem more interesting. I didn't realize this until after I stopped and I regret not getting off of it sooner.
I think I could still benefit from the right adhd drugs but it's just not worth it.