I do like the computer is more aggressive in the early game, and it can apply to the user in some cases (does that City-State have an enviable location? There's no war mongering penalty for invading early on)...but it's just way too aggressive.
And then you throw in the hyper-aggressive barbarians having better weaponry and your game can be hopeless very quickly...but I haven't struggled with this since my first couple games. It does make you change the way you play the game...and not all of that is bad. Thanks to most Civ V games starting relatively peaceful I wouldn't touch military stuff for the first ~100 or so turns, and the result was that I'd generally get a head start on technology and culture that would remain throughout the game. You really can't do that here, and I like that. Expanding is requires a bit of a cost/benefit analysis, which I like compared to the pure land grab early games of past.
...but not at the expense of constantly having wars declared on you for utterly ridiculous reasons (see Norway declaring war on me simply for not being based on the coast, America declaring war on me once for 'settling too close' while on a completely different continent than them, Montezuma getting furious the second you discover a luxury, the numerous times civs with friendship agreements would just get bored and declare a surprise war, etc....it's all a bit absurd.
Fix that stuff and the only real complaint I have is that there's a general lack of late game units and techs/civics, which I expect will be the focus of an expansion pack.