Ok playing as infected imo is totally boring. Most servers seem to have between a 20-30 second respawn delay, and even then sometimes the timer will count down and you'll still not spawn for maybe another 30-60 seconds for some unknown reason. And after you do respawn (most likely as a hunter as that seems to be the main class the game assigns) you get taken down stupidly fast, even if you do pounce on someone the damage you deal with a few swipes seems to amount to nothing.
Possibly wait for a minute to spawn then get taken down inside of a quarter that time? Not exactly my idea of fun spending half my time speccing.
I was on a map just now (some trainyard forest style map) an all we got was boomers and hunters, no smoker no tank just those two classes.
There doesnt seem to be any element of suprise in it, mainly because all the infected classes may as well be running around with 50 foot neon signs above their heads, they make so much easily distinguishable noise suprising people seems to be almost impossible.
Boomer makes an obvious grumbling\gargling\belching sound, and the hunter makes a sound like a rabid dog humping someones leg, smoker just coughs... =/ Ill give it another go tommorow but right now infected class really does seem amazingly weak, respawns are also far too long.
Its fun fighting against them for some of the above reasons but playing as them just seems to be more speccing than actual playing.