Yes, Portal 2 and Half-Life 2 are both more playable because they don't use x87 to the same extent. It's only HL that uses it heavily enough that it becomes unplayable.

Side note, I think HL2 does for physics, or something; fast moving objects and explosions cause drastic frame drops via Rosetta. I haven't been able to look into it in detail to confirm the cause.

Edit: The best "official" way to play Half-Life on an Apple Silicon machine is through Parallels, which uses WoW64's x87 translation instead of Rosetta. I've also heard you can compile Half-Life yourself using the leaked Source Engine code, but I haven't tried it myself.

x87 is different from modern floating-point, including the modern floating-point operations on x86 CPUs (SSE and later instructions) and ARM64.

x87 calculates with 80-bit floats ("long double" in C), but the host CPU's FPU typically supports only 64-bit floats ("double").

So accurate x87 emulation can't translate all operations directly to host FPU operations. It must use software floating-point on the host instead, which is much slower.