I’m overreacting, but this can hit a DM like a load of bricks if the DM isn’t planning for the experience. Just like uncle Gary’s turn resistant locales and the cleric’s turn undead ability, the urge to nerf hard makes a comeback when this spell comes into play. How do we need to react and prepare for one or more flying party members?
In 2e and earlier, flight is inspired by the complex maneuvering mechanics of wargaming, counting turns and classifying flight into different levels. Delta wrote a great review of flight mechanics back in 2012: https://deltasdnd.blogspot.com/2012/01/flying-through-ages.html.
In the comments for that article, Courtney C from Hack & Slash sums up a modern take on how we care about these things:
“Honestly, in play I don't think we've ever bothered doing anything other than just moving about how you would move if you were on the ground (with a penalty for climbing and bonus for falling).”
That fits perfectly with our modern mechanics:
3rd-level transmutation, 1 min / level
The subject can fly at a speed of 60 feet (or 40 feet if it wears medium or heavy armor, or if it carries a medium or heavy load). It can ascend at half speed and descend at double speed, and its maneuverability is good. Using a fly spell requires only as much concentration as walking, so the subject can attack or cast spells normally. The subject of a fly spell can charge but not run, and it cannot carry aloft more weight than its maximum load, plus any armor it wears.
Should the spell duration expire while the subject is still aloft, the magic fails slowly. The subject floats downward 60 feet per round for 1d6 rounds. If it reaches the ground in that amount of time, it lands safely. If not, it falls the rest of the distance, taking 1d6 points of damage per 10 feet of fall. Since dispelling a spell effectively ends it, the subject also descends in this way if the fly spell is dispelled, but not if it is negated by an antimagic field.
3rd-level transmutation Concentration, up to 10 min
You touch a willing creature. The target gains a flying speed of 60 feet for the duration. When the spell ends, the target falls if it is still aloft, unless it can stop the fall.
At Higher Levels: When you cast this spell using a spell slot of 4th level [7th class level wizard] or higher, you can target one additional creature for each slot level above 3rd.
But this approach fits horribly with our imagined joy of flight and our mechanical situations where flight dominates. I propose that flight is most enjoyed when tightly limited. This isn’t a crazy idea, video games are showing this all the time:
In Garry’s Mod, the players have a noclip button, allowing them to walk on air and move through surfaces. This is purely practical, it has minimal joy after the first moments. The objective is being able to ignore the constraints of physics entirely.
In Terraria / Starbound, the real villain is fall damage. The game world assumes a variety of exciting movement modes, such as grappling hooks with momentum, wall-jumps, invert gravity potions, jetpacks with limited fuel, and eventually flapping wings. None of these provide ‘true’ flight like Garry’s Mod.
In the recent Arkham series of Batman games, and in the Just Cause series, both protagonists have a super grappling hook and a glide mechanism. This contributes immensely to the experience. In fact, the experience itself is tailored around these tools.
So what's a DM to do?
I guess the situation isn't as bad with the new concentration mechanics in 5E. The wizard gets 1 person flying until the wizard stops concentrating. I still wonder about room for glide and grappling hook mechanics though..