NTVDM is unavailable in 64-bit Windows, but XP Mode uses 32-bit XP, so it can be used to run DOS software. (Though there will be trouble if you try to use it to run DOS games.)
NTVDM is useful, but only for the most basic software. For example, many programs do not work on NTVDM because of the limited audio and video support. You mentioned games, and I believe some of them suffer from timing issues (though this may be the games' fault for relying on a specific clock frequency for timing).
I'd say it's just good enough for the most useful 16-bit Microsoft utilities.
NTVDM is unavailable in 64-bit Windows, but XP Mode uses 32-bit XP, so it can be used to run DOS software. (Though there will be trouble if you try to use it to run DOS games.)