@Oussebon was about to report you for that first phrase
Aliens vs Predator 2 is legendary among gamers to this day and probably one of the brightest examples of sequel leaving the original in shadows. That marine campaign, still remembering being horrified of every damn beep I heard from the scanner. Brr!
Some people may disagree (me kinda included) but Baldur's Gate II was a pinnacle of cRPG back in the day. It was huge, there was no "realistic" exploration and every location was full of NPCs, quests and fight were meaningful. Not to mention the scale went from "lowly bunch of adventurers trying to not die from kobold's arrows" to "demi-gods, slayers of all that's mighty and possibly heirs to Bhaal's bloody throne". While I appreciate the different feeling BG achieved, BGII was bigger, better, stronger and nicer looking.
Carmageddon II was also "the game" that surpased the first release by a solid margin. Graphic were really good for a time and the controversy added a bit of flavour to the experience that still is rather unique. I still remember fondly as I was sneaking to neighbours house only to play on their super powerful PC (Intel Pentium and 3dfx VooDoo!) - and Carmageddon II was there. No, I didn't grow up to be a maniac killer. YET.
Hand of Fate 2 follows the same principia - better, nicer and more fun to play. Shame the studio behind this series didnt' survive the test of time, as their unique take on action RPG/table-top/card game was really fun to play and offered lots of different possibilities during gameplay by just switching few cards.
Killing Floor 2? Legend of Grimrock II? Metro: Last Light? Vermintide II? All of these were significantly better than the previous ones in well, every possible aspect.
From strategy games I would add Age of Wonders II / III and Disciples II. And Heroes of Might & Magic III > all. Don't @ me!
And as a bit of a joke. Dota 2