How would you make it?

He was way too small and easy for a final boss.

If I worked at Bethesda Studios,after getting Alduin to low health, I would of made him give a speech about how strong the Dragonborns become and say "Arrrggh...you have grown strong for a joor,a mortal, but it is time I showed you my true suleyk! Power! For I am the firstborn of Akatosh! Not even the Dovakiin can stop what I am about to become!" and then he would procede to fly upwards and start to devour all the souls of the fallen nords in Sovengarde at once and make him grow the size of a skyscraqer for a huge epic god of war/dark souls size battle, where all of Sovengarde gathers together and defends the giant hall with barrages of arrows being fired at him while you attack his head and hands due to his emmense size. And Dragonrend stops working on him since his power is too huge.

What do you think?

i wish i could of slayn him in his "mortal" flesh instead of ghost land in teh land of ghosterchiefs

I wish we could loot his bones and make a special set of armour out of them.

Dovahkiin is slain fairly easily by Alduin (who kills Dovahkiin by ripping his heart out) on top of the Throat of the World. Paarthurnax watches helplessly. Before Alduin can eat your soul, you're claimed by Shor and sent to Sovngarde. Shor is looking for generals in the upcoming war with Alduin. Instead, Dovahkiin claims Shor's Heart (against Shor's will?) which had been with Shor ever since the Nerevarine defeated Dagoth Ur, believing that Shor doing battle with Alduin directly causes nothing but the kalpa cycles to continue. And because you need a power source.

You could back to Nirn, and fight Alduin again on the Throat of the World. You kill him, and devour his soul before Bormahu can reclaim it.

(Then, maybe, something happens that makes Dovahkiin normal powered - at least until his mortal body dies. Maybe you lose your connection to the Heart of Lorkhan?)

Right now I'm just throwing whatever comes to mind down. So forgive me if it doesn't make sense.