Death Note is probably my all-time favorite anime, but this is an insanely tough question and there are so many amazing shows that I wanted to list 10 of my all-time favorites.
Berserk - The first anime outside of DBZ I watched and what got me hooked on the genre.
Code Geass - seriously flawed, but the closest thing I ever found to Death Note and a perfect ending.
Samurai Champloo - Beautiful in every way and the likeness of the protagonists and my brother and me made me fall in love with this show.
Steins Gate - Brilliant and the second anime I watched. Berserk pulled me in and this sealed my undying love of the genre.
Cowboy Bebop - An absolute classic and with how well written, acted, and drawn it was, it mostly avoids that overly dated feeling that comes with shows from the same period.
Hellsing Ultimate - I loved this show to begin with, but like DBZ, it was made infinitely better by TeamFourStar and their abridged series. Anyone who's a fan of the show and hasnt seen it should do it now.
Monster- Gritty, dark, suspenseful, and gorgeous. I watched this only once and during a pivotal portion of my life. Maybe it wouldn't hold up if I watched it now, 10 years since the previous viewing, but I want to believe it would.
Hunter x Hunter- Easily the best and most memorable Shonen there is. I know we're all praying this will be completed some day and even if it takes another 20+ years, I'll be just as excited as the first time I saw Gon punch Hisoka.
Full Metal Alchemist Brotherhood- I loved the original but even as a non-manga reader I was devastated by what they did to it. They redeemed it so hard and this show was fucking perfect.
And #10 is a copout, but I gotta do.
Shonen in genea - As much as I hate aspects of the genre, I absolutely fucking adore it overall. Even when it's bad, boring, or lazy, I still find enjoyment in it and get sucked in during the epic moments. Whether it's the older YuYu Hakusho, which is almost hard to watch, the middle Naruto/Bleach, or the new school Fire Force, Black Clover and My Hero, I fucking love them when they're good and I'll deal with the filler and the boring as ass end arcs because they've already sucked me in.
Honorable Mentions
Attack on Titan - I need to see how they finish this. If it's half as fo as I hope, it'll make the top 10.
Demon Slayer - This could be on par with HxH if it continues the way it has, but need to see more.
One Punch/Mob Psycho - Both are amazing and funny, but not funny enough or engaging enough for top 10 yet. We'll see how the anime progresses.
Parasyte- I don't have a single bad thing to say about this show. It should probably be on the list, but hard man.
JoJo - JSP finally convinced me to watch this masterpiece and ai am eternally grateful, you guys rock for this one.
Future Diary - What can I say, I like fucked up shit.