As far as your own character goes, level ups give you skill points to spend on skills both combat and utility, which tiers at 30 point increments giving you new abilities, which can be really important (like being able to craft even the simplest ammo, upicking locks, and so on). You also get Perks every 3 or 4 levels, and those can be both powerful and well written (one that gives charismatic characters more endurance justifies it by saying that you spent so much time convincing others that you're a badass, you managed to trick yourself).
