It's more like a 2.5, and initially I was going to round up to 3 stars, but the more of the review that I wrote, the more that I realised rounding down was going to be more accurate.
Remember in the show how Hiro is a massive pervert and comes across as a total incel? Yeah, me neither, but apparently that's the vibe that the author wanted to go with for the book. Pretty much his every inner thought was objectifying the women around him, whether he was into them or not. Working alongside a larger lady? Better have internal dialogue about how her breasts are like shelves. Flashing back to a career meeting at high school? Better stare down the lady's top. Charlie touched Hiro's arm? Well that certainly warrants a two page vivid description of him getting a boner. I wish I was joking.
Also, as a hardcore fan of the show, I was frustrated by the fact that this book made so many mistakes not just in terms of how Hiro's power works, but even in things to do with specific events along the timeline. It was as though the author hadn't watched the show, and had only watched the relevant episodes with Hiro and Charlie, and read a quick summary of the rest. I'm really picky over consistency, and so it was frustrating when events happened in the book that had already been shown in the show, and the book had them play out differently.
I also found that the writing style was somewhat sloppy. The author chose some really bizarre tangents to go off on, and the bits where they were recapping show moments were written so boringly that I nearly DNF'd after the first 2 chapters, and the only reason I kept going was because I'm a huge fan of the show and wanted to know more about Hiro's story. However, it did get a bit better as the book progressed, and wasn't unbearably poorly written, just not to my personal preference. I think one of my main gripes was really with the bad logic in a few places. The author wanted things to happen, and so they wrote them without giving thought to whether it was possible or not. For example, at one point Hiro and Charlie play chess, and the author describes some of the moves. That'd be great, except it's clear that the author doesn't really understand how chess works, because they described a win that would literally be impossible as the pieces wouldn't be in the position described in the win given the other moves that had been described.
I just feel that a book written about an established character with superpowers should pay better attention to how those powers have been described in the show. Clear limits are established, and yet in one scene we have Hiro pouring coffee whilst time is stopped (his power freezes liquid, so the coffee should not have moved), and we also have him driving a car whilst time is stopped, which again wouldn't work as we know that the engine is also frozen.
However, there were a few interesting moments, and it was nice to see the relationship between Charlie and Hiro develop, even if some of Hiro's inner thoughts were a bit creepy. Like, at first I was like 'Charlie deserves better', but then she did a few questionable things and you're like 'eh, I guess they deserve each other'. One of the things I quite liked, that wasn't mentioned at all in the show, was that there was a sub plot of Hiro randomly teleporting away to different events in the past, and at one point we see him meet Molly's dad, which was pretty cool as obviously we only see the aftermath of Sylar in the show, and so it was a surprise to see her dad mentioned.
The ending was pretty emotional, as Charlie makes a big decision and allows herself to get killed because she knows it's necessary so that Hiro can go and save the world. It's an incredible moment of bravery, and it's also a moment that haunts Hiro because he loves her, and he's forced to let her go so he can be a hero, it's very poignant because in many ways it mirrors his favourite story from when he was a kid, of Takezo Kensei and the Dragon.
However, the biggest twist of the book was when I got to the very last page and realised that the author was a woman! The writing was so stereotypically male in the way it objectified women and described them by their breasts, and I just couldn't believe that the book had been written by a woman.
But yeah, overall I wouldn't really recommend this, but if you're a huge fan of the show and you desperately want to know more lore in regards to Hiro's journey, then I guess you could slog through this and it wouldn't quite be THE most painful read ever. But please don't delude yourself into thinking this is a good book, because it really isn't.