Halo PC does have a feedback system. It's very subtle but there's a noise when you hit somebody. I'm pretty sure the trial does it as well (I'm installing it right now to check). It's just loud enough to let you know that you're doing something right, even if you don't realize it right off the bat. It might not be anywhere near as obvious as Call of Duty's hitmarkers or impact sounds, but even something so subtle that it goes unnoticed by most is enough to give you a far better feeling of feedback and "oomph" than the later games, where feedback is completely nonexistent outside of shield flares, and even those can be inconsistent (or non-existent, in some gametypes).
The first halo didn't need a "feedback" system.
Edit: Just checked, the Halo PC Trial has it as well. Easier to hear with Plasma weapons.
By the way, if you're looking for some easy kills, playing on the trial servers is akin to shooting fish in a barrel.
Edited by Drew, 14 April 2011 - 10:33 PM.