Battlefield 1942 was revelatory but Vietnam was the one I truly loved. Asymmetrical warfare FPSs.

e: I was also a huge Day of Defeat stan but like no one played that game so I didn't bring it up.
What was your favorite class? I started out on the MG42 and moved over to being a Kar-whore (Axis rifle). So deadly.
I want to be a hipster and say the FG42 class, but sheesh that gun was bad. (Especially the scoped one.
)
I liked to skirmish, so the Sturmgewehr and Tommy gun were my bffs. Sure I'd get sniped 4/7 times before I did any damage, but those 3 times where I could sneak around and flank a group of enemies and kill them all... 
The K98 was truly a beast. 
There was a period where the railguns were the only truly viable option.
By the time of Source I had moved to the STG44/BAR combo. Then reached a transcendent level with those in Source. You only need three-four and two shots to center mass respectively so once recoil ain't no thang...
It's unfortunate that Source never got the love, and maps. Especially Saints, Merederet, Northbound, Escape, Flugplatz, Glider, original Jagd, etc.
Every so often I pop into Donner/Kalt/Avalanche/Flash and cause havoc flanking around with those two guns. And their two grenades.
Especially the nades. Though I don't remember the fuse times as well as I used to.
In like 2007 you did not want to have your entire team on a center cap point where I knew how to throw over a building/arch out of sight right onto it is all I'm sayin.
Used to do it in DoD too but I would miss picking it back up after throwing it down it felt like half the time. There was one map in that where if you threw it right to hit the "roof" it'd drop right down onto center point...delicious.
I'm glad the steam stats don't go back before 2009, now it only looks like I've played a combined 12 hours of DoD and DoD:S ever. Something similar with TF2 which replaced DoD:S...thanks Valve!