Are you playing objective gametypes?
My best game was probobly Modernwarfare 1, then black ops, then modernwarfare 3, then 2, then black ops II.
I was unstoppable in MW1. Black ops was also a beast, calling in multiple chopper gunner/dogs/blackbirds. Modernwarfare 3 brought specialist bonus, which when I got it with the silenced mp7 I was UNSTOPPABLE, getting multiple nukes a domination game.
I am playing my best in this game. I just started fps games bout 6 months into bo1. I had a wopping .82 in that game, a 1.1 in mw3 and now I have a 1.66 in bo2. I have finally got map awareness and accuracy is getting better every day. Now I just need to win more gunfights and my game would be complete. My reflexes aren't what they used to be so I have changed my playstyle to use an ar and attack from mid-range and try to stay away from extreme cqc when I can because in this game I find it harder since the players move so fast. I'm happy with my 1.66 because I realize how far I have come and the fact that I run support streaks and pto always. If I ran lethals I would probably have more kills.
I have been very consistent through the years
COD3 50,000 kills and about 4,000 wins
COD4 1.50 K/D 1.50 W/L 70,000 kills
waw 1.70 K/D 3.50 W/L 110,000 kills
MW2 1.50 K/D 6.00 W/L 120,000 kills
Blops 1.60 K/D 7.00 W/L 20,000 kills---Hated this game
MW3 2.15 K/D 11.00 W/L 95,000 kills
Blops2 1.80 K/D 3.50 W/L 38,000 kills
My K/Ds haven't been the best really in any, but as far as helping the team, winning, outsmarting opponents, etc., I'd say Call of Duty 4 and this one. In Call of Duty 4 I would look forward to the opportunity to have to take out 5+ enemies alone if my teammates died in Search. I still do enjoy the opportunity but especially back then. I think this one, with league play and even some GB matches, I'd probably be better able to compete with the better players overall, with more refined tactics, better aim and reflexes, line of sight recognition, etc. Black Ops 1 was awesome too but I didn't play it as much when it came out because I was living in a dorm and couldn't play online lol
PS to the OP, I like how you call your 2.5 KD "low" lol It's not just you that does that but many others, even though they know that's a good KD, it may not be a 3 or 4.0 but its still good, but they'll try to act like its bad and it kind of comes across like they (not you) are bragging about a K/D in some underhanded way. It's like Tom Brady saying "I only threw for 5 TDs that game? That's terrible" haha