The kettle is so versatile, it's a joy to cook on and I've tried plenty of others.
In terms of initial starting costs vs variety, ease and quality of food you can do, there's no comparison. Sure a different type of bbq may do one thing slightly better or easier, but that same BBQ can't do the other styles as well as the weber kettle.
You only need 1 kettle to do any type of BBQ, but the addiction kicks in and 1 is never enough!