Mega Man X, the first game has the perfect difficulty balancing, weapons, level design, and is just more fun than the others in my opinion.

this is going to be contentious, but ratchet and clank

The Legend of Zelda >:)

999

Paper Mario

Mario & Luigi: Superstar Saga. It's remarkably polished and kinetic for a first try at a battle system, and in particular, the Bros. system has a particularly snappy punch to it that the latter games completely forgot about. On that note, latter games in the series revel in particularly drawn out and repetitive setpiece boss battles, usually based on some sort of hardware gimmick. This first game is completely lacking in such foolishness, and because of it cuts a quicker, more enjoyable pace overall.

Doom

It is of my personal belief that Drakengard can sit here.

bowsers inside story is better than superstar saga

Xenoblade Chronicles

Telltale's The Walking Dead and Valkyria Chronicles. Season 1 of TWD was peak Telltale both because the concept was newer to everyone, but also because the story was just better written with less contrived feeling conflicts. Valkyria Chronicles was a great anime style WWII tactics game with a surprisingly mature story, and apparently the sequels turned it into a high school anime game.

the shining series for sure (specifically shining force), camelot stopped making them after the third force game and the series devolved into a really shitty mess of bad spinoffs and flavor of the month anime games after that

Since MMX and Parasite Eve were already mentioned, I'll go with Splatterhouse. The rest of the series did away with the sheer sense of consequence the original had, which was very impressive to see in such a classic. Every single weapon placement feels perfectly thought out with the dual shotgun trick in particular being just enough for Biggy Man, but the default punch and slide are a really neat example of less being more as well. Even with so many enemies having varying patterns it always feels like the player has just the right tools to deal with them. Not to mention the hypnotic music and excessive gore really add to the game's uncanny nightmare like vibe as the player desperately attempts to survive. Truly one of Namco's greats.

Spyro 1. Its sheer sense of space makes its sequels look like they're almost ashamed to be platformers by comparison.

Suikoden. Not a lot of people think that 1 is the best one but it's a game that is overflowing with charm and makes most of the 108 main characters interesting with the little dialogue they have. It also has the most tragic protagonist in the series which people tend to ignore.

Definetely Deus Ex. F.E.A.R too

twewy is a low-hanging fruit but twewy

With you on a lot of these, hombre: https://www.backloggd.com/u/DJSCheddar/list/series-where-the-first-game-is-still-the-best-1/ LOL

Not gonna be a dork and say "all of them from my list that you don't have" so I'll stick with one contentious suggestion: Silent Hill 1. It feels the most complete and has a perfect balance of scares, gameplay, and the series trademark psychological stuff. SH 2-4 all succeed at those things as well but in different amounts.

x-com: ufo defense
quake
r-type
xenogears, if we consider the miserable xenosaga things to be sequels...

oh shoot dude I didnt realize this idea had been done before, that's cool

I'd argue Xenogears should not be here at all as Xenosaga is a spiritual successor.

Twewy literally only has 1 sequel and its badass are you out of your fucking mind

if we're including tiny series' like that might as well include Chrono Trigger as well. Technically it's 4 games lmao

Belated thanks, I added a couple more to my list based on this. Great minds think alike!

Gotta agree with Katamari Damashii.

WarioWare: Mega Micro Game$