Book. Masterpiece. The Foundations series by Isaac Asimov Space Odyssey series by Arthur C Clarke Dragons of Pern series by Ann Macaffey Skylark by DD doc' Smith Lensman by DD doc' Smith H3G3 (not recommended unless your mind was built with 95% unobtainium) Disc World (highly not recommended unless your mind was built with 100% unobtainium)
Since you read the Nightside series by Simon Green, you might as well read his Deathstalker series and the Secret Histories series. There is alot of overflow from the Nightside in those, especially Secret Histories. If you can find them you might want to check out the Matador series by Steve Perry. They first book is called the Man Who Never Missed. Then there is the Cal Leandros series by Rob Thurman. I'd also recommend some other stories mentioned in this thread. Galactic Dark Net, Terror Infinity, and Iron Teeth: A Goblin's Tale.
It is an absolute travesty that no one has mentioned the Vorkosigan Saga by Lois McMaster Bujold. It completely fits the OP's request for a long sci-fi series with male MC. Books listed by in-universe chronology: Falling Free Shards of Honor Barrayar The Warrior's Apprentice The Vor Game Cetaganda Ethan of Athos Brothers in Arms Mirror Dance Memory Komarr A Civil Campaign Diplomatic Immunity Captain Vorpatril's Alliance Cryoburn Gentleman Jole and the Red Queen There are various compilatory volumes that you can get that combine the books too.
Second the recommendation for Vorkosigan saga (although the male protagonist stories only really start from The Warrior's Apprentice onwards. Books 2-3, and Book 16 are about his mother.) Also, try Jack Campbell's The Lost Fleet series. Military Sci-fi. The RCN series by David Drake is also another interesting military sci-fi series, though it balances protagonists equally between a male ship captain and a female librarian/spy. The first book (With the Lightnings) is free to download and read from the publisher. For alternate history/fantasy series, try Naomi Novik's Temeraire series. Dragons were not wiped out, and instead exist in all cultures and continents in various relationships with humans. As Napoleon attempts to conquer all of Europe with his dragons, the British forces intercept a rare dragon egg from the Far East and incorporate the new dragon into the Royal Air Force Dragon Corps in the Battle for Britain.