I've played this dlc just two times and it is only for one reason. When I played it first time, I played an cruel orc obsessed by power and it was ok for me that I've became a champion, or in my opinion "slave", of that tentacle kind of thing which someone call daedric princ. But, well, durrign my second adventure of solstheim I wanted to decide not to help haemus mora or just not side with him. Just kill Miraak and go away like dragonborn with no bounds to any octopus-portal-being. But then, during questline, I've realised, that I have no choice to refuse his services or his help and that make me little bit... nervous(?)

It is roleplaying game, so why I can't refuse badguy's help?

Anyway, my question is: It is just my wrong playing or you can decide to leave haemus services after or even before killing miraak?

Nope, helping Mora is the only way to stop Miraak. You can still mouth off to him and basically rail against him along the way, but you need to help him to finish anyway.

If you want choices you either need to mod Skyrim heavily or just play an earlier TES game.

I think Hermaeus Mora wasn't too bad in the Dragonborn main questline. It certainly didn't leave a foul taste in my mouth like with some other daedric princes. There's no soul selling or killing innocents.

Miraak is in H-M's realm. You can't go there without his help, so you have to go along with that. But when Miraak is dead, you're not tied to doing anything more that H-M asks, any more than you became Gjalund Salt-Sage's thrall by taking the ferry to the island.

yes but it's a little bit shame that there is only one way how to deafeat main boss - even alduin can by slained with help of those dragon-monks or blades so why am I forced to side with this daedric princ. For example, why I can not just choose to help skaal people to destroy miraak?

My elf became disgusted with dealing with 'Jabba the Hutt'. She felt like she desperately needed a bath after every time he talked with her. When Jabba wanted her to betray her friends the Skaal, she on the spot aborted the questline and walked away in disgust. The questline takes 'the ends justify the means' far far beyond the pale. If that's what it takes to 'save the world', the world is not worth it. I consider the questline basically unplayable except for characters that are either evil or gullible enough to sell their soul to a slimy octopus. Some folks don't have a problem with it, but I do.

I just put it down to bad game design, and allow my imagination to override it. I've found that I need to ignore a lot, or use mods (or do both) in Skyrim.

When I first started playing the game, I was put off by a lot. I've since realized that it's my game-play, and I get to say what "really happened."

This is my attitude too. Not only in Skyrim, but in all the games. In order to craft the game experience I want for myself I've had to ignore chunks of Morrowind and Oblivion too.

This will probably sound like a backhanded compliment (or a forehanded insult) but one of the things I most like about Bethesda's games is precisely that I can imaginatively wave away those parts of the games that don't fit my character's story. I don't feel as though I have the freedom to do that in a lot of other games.