I never really had any problems with lag, but then I always set my filter to only display games with good ping. I did play one game which had some serious lag problems, but I quite it, gave it a low rating, and joined a better game instead.
Personally, I like how the slots are set out. It means that players who are a higher level (and thus are already better at playing the game) won't get an unfair advantages over new players, but they do get the option of specialising in one particular area.
Things I'd like to see:
-- A better way to swap your weapons. At the moment it's really hard to quickly swap to grenades, which means that you're often miss the oportunity that had presented itself to you.
-- The ability to regain your health. Maybe leave one or two rations lying about?
-- The option to use the sixaxis tilt controls to aim grenades (like Uncharted).
-- A greater variaty of clothes and stuff to chose from when creating your character.
