Depends on the game & if you're talking digital only or game cart. Some higher end digital games like Code:Realize, Disgaea 4, Final Fantasy X, MGS HD Collection, etc are 3gb-3.5gb in size. When you figure formatting loss, misc loss due to OS, & save game sizes, I don't think 4gb will quite cut it.
(This is all assuming legit system w/ legit games, "backups" on a CFW I can't comment on)