There's no initial save! Legendary resistance wouldn't do anything for the first round! 

This spell really is the perfect example of the comments on 90% of the spells on this site. 

Just a bunch of people complaining that it's a terrible spell for its level, and a bunch of other people complaining that it's insanely OP. Lol.

its just entirely situational.

Hypnotic pattern is good against a lot of low wisdom enemies,

Hold monster is good against a single powerful enemy that nevertheless is not likely to make its save.

Otto is good for something so powerful that its worth your caster doing no damage and just debuffing it, because it is going to take the combined might of the whole party to fight. Yes enemies like this definitely exist, and they will shrug off your hold monster with their high save and legendary resistance like its nothing.

Its like that famous post of how someone complained that Tiamut's stats are not that good because you could just polymorph her. Yeah, if you can force her to fail enough times to burn through the legendary resistances despite good wisdom and all round stats? maybe an entire cabal of very high level wizards working together could polymorph her, and honestly that feels about right.

this spell is like so fun, but I hate that it is such a high level spell which you only obtain until level 11, so for lower level campaigns that I mostly play I never have the opportunity to use it.

So it's the sort of "restrained" condition but better

this the boogie bomb spell

I think of this spell everytime I watch Shrek Forever After with my 6 yr old when the Pied Piper makes the Ogres dance.

For a 6th level spell it is INCREDIBLY underpowered... but I don't use it for power... I use it... BECAUSE IT'S FUNNY!

There's no initial saving throw, I assume that's the big thing. It bypasses legendary resistance and works on every creature in the game that can't be charmed with no save, even if it's for one turn that simple thing makes it way more powerful. 

This seems similar to Command: Dance, but with no save untill their turn

Time for Mambo #5!

Hold monster only works of the creature fails the save. Otto’s Irresistible Dance automatically takes effect and only persists on a failed save. On top of that, to attempt the saving throw is the creatures entire action.  

What am i missing. This seems verry weak for a 6th level, right?

No movement and disadvantage on their attackrolls. Isnt this strictly worse than hypnotic pattern for example?