I think it's unfair to compare to 'All the Young Dudes', because although they share similarities in plot and of course, characters, this is nowhere near as great. Hell, it's not even good.
'The Marauders' by Pengiwen is a tome, a colossal series following the characters of the first wizarding war (and admittedly, my favorite era) through their first year at Hogwarts.
My main issue with the novel is the characterization. I am no stranger to the difficulties of writing fanfiction, having to understand somebody else's characters inside and out, and I have respect for the attempt. However, the personalities of the four boys were not only bland and lackluster, but I was completely unable to distinguish them. They didn't feel like themselves for the majority of the novel and were even somewhat unlikeable at times. Sure, there were a few funny lines, there had to be in a 1400 page book, but it in no way overshadowed my sheer disappointment.
Pacing, another thing I was disheartened by, was incoherent and quite frankly, a state. Long, scenes, unnecessary chapters, finally getting somewhere then coming to a halt. I spent most of my reading experience utterly bored out of my mind.
Additionally, the focus on other characters took me by surprise. The attention to Bilius and OC's was rather upsetting as it can be inferred from the title that the book will follow the marauders, not other students at the school. Perhaps this is personal preference and my indifference to the other characters, or maybe this is the opinion of the masses.
In conclusion, my disappointment is tangible and my rating low. Would I recommend this? absolutely not. Don't waste your time, there are much better fanfictions out there.