This fanfic defies a lot of conventions of the genre, and I think that's what makes it so awesome. The main character is Lexen Chelseer, an OC, but don't be turned away by that fact. Lexen ends up taking the place of Harry Potter, and is (as far as anyone but Dumbledore and select others know) that character, just with a different background and motivation. Lexen is an interesting character, with the unconscious ability to travel back in time a day (or under rare circumstances, more) every time he dies. And trust me, Lexen dies A LOT.
He goes back in time to right things that go wrong, just like every other Peggy Sue story, but the interesting bit is in the granularity of these loops. Where the usual Peggy Sue protagonist has only one chance to get things right (and by extension, only one chance for the author to make things go horribly wrong), Lexen can come to a catastrophic end without the story itself ending. Things go wrong, often in unique and interesting ways. People die. The story is currently on its second 'loop' through the books, with the first take covering first and second year. There were quite a few surprises that take, and this one is shaping up to be even more different.
What makes this fic particularly fascinating is that given this basic formula, Keolah manages to twist and distort the canon plotlines while remaining very in character. The best part about reading this fic is those moments where, suddenly, all the canon expectations are completely subverted. Characters die. Alliances are made and broken. Valuable artifacts are surrendered to the enemy. And it's anyone's guess what happens next.
It's well worth a read. The grammar is good, and the pacing is excellent. Even better is the update rate, which has been near-constant since the author started. In a little over a month, she's written 100k words, and doesn't seem to be slowing at all. So go, go and read it. It's definitely worth the time.