Marshall pride!
Glad you're liking it, it's a good gun that deserves to be used. Everyone that says it's not effective just can't use it properly.
Using the Marshall isn't like using other guns, it's a must to be quick and agile, power jumping and sliding to get within it's range of effective use. After a kill with the Marshall I usually power jump and spin around to scout out for any other enemies.
Oh, and you should try sliding more often! It's great when you get used to it. When you slide near another player, your character automatically kicks, dealing a melee hit. It's very tactical since it drops you down to dodge, BUT it does knock you out of cloak if you did so while stealthed. So uncloak, slide, shoot 'n' kick. It makes you feel like a superhero.
And the feeling you get when you get a good one-shot with it.. just awesome.