I mostly just play by myself
Oh, might I ask why? Nothing against it, to each their own, but I always figured KF was better when played with strangers. As a side note though, you must be pretty good. I always believed KF was much harder when played alone.
Most of the reason is that I've run into enough ass holes in co op games who will complain when I'm not doing the specific thing they want me to do. I've played a small bit in multiplayer in random servers and the majority of people I ran into were okay, others made me want to headbut a wall because 'why didn't you fucking do X? You made us fail!' or 'Dude why didn't you pick up my fucking equipment?! fuck you!' or other crap. I'm sorry my gear weighs a metric fuck ton and I'm the fucking medic carrying a medigun and a bloody shotgun because nobody protects the fucking medic.
Also, as far as being good, I'm probably terrible at the game, rarely play solo outside of beginner difficulty, occasionally on normal. Beginner makes everything easy as shit but I get to use the cool expensive guns I can't get when I play on normal because I evidently suck. Also, can confirm the game is harder solo on any difficulty except beginner.
EDIT because and I accidently wrote ways instead of weighs...
Also another reason I haven't played a lot of multiplayer is because I'd like to at least get a couple of levels in the perks I prefer before really hopping into a lot of multiplayer, though with the crap way you level perks in the game I'll probably abandon that goal.