Some people have called the Miraak fight an anti-climax, and nothing really special, based on things I've read. In one aspect, I agree. It could have been more... special? But, honestly, it was still the best major fight in the game for a few reasons. Namely, this is because I didn't have abilities that would just wipe him out. With Harkon, I used Slow Time (one of my signature shouts, next to Soul Tear) and... well, you know. Plus, Serana was there, and he had some minions to help him.
I usually don't like it when monsters regain life points. Mercer Frey doing it was especially annoying. But it seemed done well enough with Miraak simply because of how the fight was set up. I got to use a number of shouts, but if I used one like Slow Time, I would have only knocked him out completely with it once. He would have just regenerated.
If you don't try to work to your hardest and make use of strange advantages in the game that let you kill Ancient Dragons without taking damage, the fight can be somewhat fun, if not hard - and it's the fun that's most important, honestly. Just run the narrative in your head in the process and its a lot better. Add your characters lines of dialogue in.
Hit Points are more than just a characters life; it's all the other factors besides that. After all, your character can't really survive being bitten in half by a dragon, no matter how well armored. With Miraak, I went about it that way. Everytime he absorbed the Dragon Souls, he was just recharging himself. On the second dragon he butchered, I drank the White Phial to gain back 100 LP. Not because it was the best potion, but because it was small, and all my character could really pull out in that brief span and actually go back in immediately.
As I saw it, the fight was an even match, and neither my character nor Miraak really took that much damage in the short few minute span that it took. It would have gone on much, much longer if Hermaeous Mora hadn't intervened with the tentacle.