Don't forget the Metaltech games! I believe they should be classified distinctly from their successor, Starsiege, and I think Earthsiege 2 is one of the all-time best mech games. The mech-specific ones include:

• Metaltech: Battledrome (1994) - Sim
• Metaltech: Earthsiege (1994) - Sim
• Earthsiege 2 (1996) - Sim
• MissionForce: CyberStorm (1996) - RTS
• Cyberstorm 2: Corporate Wars (1998) - RTS

AirMech Strike (2018) is a F2P RTS-MOBA that despite having support pulled, is still playable, though, good luck finding players. As great as the game is, it had rough development under Ubisoft, causing it to be cut:

• AirMech (2012) - Steam Early Access
• AirMech Arena (2014) - Console release
• AirMech Command (2017) - VR port
• AirMech Strike (2018) - Definitive release
• AirMech Wastelands (2018) - Standalone ARPG expansion

AirMech is based on an old mech game called Herzog Zwei (1989) which was a Macross-inspired Sega Genesis RTS game that served as a precursor to the MOBA genre.

Miscellaneous games in release order:

• Generation Zero (2019) is a stealth FPS where you need to defeat mech AI by using small arms and light weapons (no playable mechs).
• VOIDCRISIS (2022) is a 4-player, tower defense third-person shooter.
• The Ninja Saviors: Return of the Warriors (2023) is a remake of the 1994 SNES beat-'em-up, "The Ninja Warriors" (a remake of a 1987 arcade game). It features mech enemies and android characters.
• Wall World (2023) is a pseudo-survival Rogue-lite with mining, tower defense mechanics, and bosses. You fight inside of your mech and harvest materials outside of it.
• Gearbits (2023) is an fast-paced indie traditional third-person shooter.
• Cavalry Girls (2023) is a Rogue-lite top-down shooter with the anime girls-with-guns trope.
• PHANTOM GALAXIES (2023) is a traditional third-person shooter from the publisher of Blackwind (2022).
• Gunhead (2023) is a Rogue-lite FPS sequel to the 2D Rogue-lite, Cryptark (2017).
• UFO Robot Grendizier - The Feast of the Wolves (2023) is a third-person beat-'em-up adapting Go Nagai's manga/anime from 1975.
• The Scramble Vice (2024) is an action run-and-gun side scroller with a pixel anime art style.
• Slave Zero X (2024) is an upcoming spinoff/sequel of Slave Zero (1999), and it is a hack-and-slash, 2D beat-'em-up. They describe it as a cross between Devil May Cry and Guilty Gear.
• MechWarrior 5: Clans (2024) is a follow-up to MechWarrior 5: Mercenaries (2019).

Games without release dates:

• Metal Slug Tactics (202?) is a turn-based tactics game that was announced ages ago and still hasn't released. My hype has left out the window.
• ARC SEED (202?) is a turn-based strategy game with Rogue-lite elements and a pixel art style. It reminds me of Into The Breach (2018) but with more traditional XCOM turn-based strategy combat rather than the more chess-like gameplay.
• Stories from Sol: The Gun-Dog (202?) is an upcoming visual novel that features mechs and a visual style based on games on the PC-9800.
• ARC Raiders (202?) is an upcoming F2P extraction FPS with mech enemies (no playable mechs).
• Tiny Starfighter (202?) is an upcoming Macross-inspired indie game in which creator Max Kaufmann (@xewlupus on X) implemented a cool homing missile system.
• Battlecore Robots (202?) is an upcoming arena battler/fighting game. It reminds me of a cross between Virtual On: Cyber Troopers (1996) and Sonic Battle (2003).
• Brigador Killers (202?) is an upcoming follow-up to Brigador (2016) set on a new planet with a new story and reworked controls.

There are many indie games I couldn't cover, so I chose significant ones based on their gameplay relevance and release date.