A bit cliched. The whole Dumbles betrayal, Hermione/Ron cutting him off, Merlin heritage are a bit used.
Then again, 95% of fan fiction is cliched so whatever!
I think you can wriet pretty well, you have good flow and grammar. I am interested to read this story.
Two words of advice (metaphorically speaking): First, avoid more cliches. Perchance make it so Harry isn't a descendant of Merlin, just that Merlin looked through time and saw Harry needed help.
Second: Write longer chapters. Id rather you update less often with longer, more detailed chapters.
Keep going, and keep trying. If this is your first story, then do what you wish. MY first story was a piece of crap!