Playground games. Forza Horizon has been amazing for well over a decade now. 

Obsidian consistently puts out amazing games. 

Insomniac has been going strong since the PS1. 

Sucker Punch has been on a roll since Sly Cooper on the PS2. 

I can't really name a bad Zelda game outside of the CDi stuff. 

Mainline Mario games have always been a treat. 

Gamefreak fell off with the release of the Switch Poke'mon games and the gutting of the full Poke'dex. 

Bethesda's game design is cookie cutter and bland. 

Halo doesn't have the same developer so maybe this doesn't count but Halo 4, 5, and Infinite are pretty weak compared to Halo CE, Halo 2, Halo 3, and Reach. 

Gears of War has really fallen off, especially with the addition of microtransactions. 

Konami is almost nonexistent these days. 

Blizzard is not the same company anymore. 

Phantom Hourglass is a pile of shit.

Nintendo and Capcom are the top dogs. Nintendo goes without saying but Capcom made so many great games for the Coin-op arcade back in the day and they continue to make great stuff throughout the console and digital era.

If I'm going to mention a studio that fell off then I will always talk about SEGA. They are the only company to give Nintendo real legitimate competition. They were able to match Nintendo game for game. No DVD gimmick, no proprietary media hubris blunder, no wiffing on your audience, just game vs. game. SEGA also made spectacular games in the coin-op arcade era. Outrun, Hang on, Altered Beast, Golden Axe, Virtua Racing, Virtua Fighter, Crazy Taxi, House of the Dead.

The Dreamcast was my favorite console of the 6th generation, regardless of it failing. The 2k sports series SMOKED Madden! If not for SEGA having idiots in their front office making horrendous marketing decisions, they would be competing for gaming supremacy with Nintendo and giving them a run for their money.

I would also mention Midway. They were godlike in the coin-op arcade era. Spy hunter, Super High impact, NBA Jam, NFL Blitz, Arch Rivals, Mortal Kombat, Gauntlet legends, Wrestle mania Arcade.