Having played 5e I greatly disliked concentration. Nearly all good spells were given concentration so you couldn't use more than one at a time; wanted to haste the fighter while flying away from an enemy? Too bad, both are concentration. So a lot of my 5e combats were just picking the most powerful concentration spell I had then firing away with a cantrip every turn and I was incredibly bored. Eventually I found out that blindness wasn't a concentration spell so I cast that sometimes but was generally unimpressed with the results considering it's a CON save ends spell, generally the worst thing to target.

If you want to make spellcasters both worse and boring it's an interesting idea, I guess. It would take more work than just switching the mechanic over though because, ironically, most combat spells in 3.5 that take concentration aren't even worth casting if they didn't have it.