While "concentration" is part of the 5e rules, i still wonder who thought that up. Or at least decided which spells require concentration and which not.
Since this is my first contact with 5e rules i was...surprised...to say it mildly. There are some spells/rituals where i can understand and accept such a mechanic but to think that a cleric can bless 3+ people OR give one person a Shield of faith is...BS

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Spells like the "hold" line get ridicoulous this way. The victim gets a save each turn AND in addition his friends can just pummel the caster till he fails his CONSTITUTION save. Most casters surely have tons of that...
(Just fyi some enemies get their save at the beginning of the turn and can even act when they succeed, i forgot which fight it was but it seriously annoyed me. i think it was that "spike" guy)
So if some rules from 5e are ignored or changed please let this be one of them. Or keep it for spells that need actual effort AFTER the casting. Divination for example.
It really grinds my gears to see that you can conjure a blob of magical grease and then look elsewhere but to conjure a for of magical darkness you need to concetrate until you get slapped or the time runs out? Eh?