The controllers pose no problem for me - my hand doesn't cramp, and I find them pretty responsive and accurate. Games like Thunder Castle and Night Stalker hold up really well. Yeah, a lot of Inty games do feel slow (Space Hawk for one), but on the plus side the system just has so many unique, quirky games in its library.
Yeah I feel the same way, kinda surprised at how many struggle with INTV controllers the most of all consoles. Where I find 5200 ones make my hands hurt (doesn't fit my palm right) and 2600 joysticks can be too stiff for Summer Games, Decathlon, Soccer etc... and break too easy. The Intelly controllers do the job for me. My emulation (PC controller) scores aren't any different or better.
The only two games that did any kinda cramp was Dracula (disc), and Space Armada (fire). My thumb would get tight from having to chase people around in Drac, and then the firing constantly in Armada would sore up my thumb. Never had a problem besides these two games though, Mattel was smart enough to include auto-fire.
Speaking of early 80's, it was either substance... "Intellivision/Colecovision" or simple pick up 'n play games with speed and no slow downs, Atari 2600/Odyssey2.
It's hard for me to choose between 2600 or Intellivision. Both win for different reasons.